seeds: fix compiler warnings on linux & windows

these were the warnings:
/builds/precommit_linux64/opencv/modules/imgproc/src/seeds.cpp:1003:50: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
/builds/precommit_linux64/opencv/modules/imgproc/src/seeds.cpp:1004:46: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
/builds/precommit_linux64/opencv/modules/imgproc/src/seeds.cpp:1005:50: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
/builds/precommit_linux64/opencv/modules/imgproc/src/seeds.cpp:1006:50: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
/builds/precommit_linux64/opencv/modules/imgproc/src/seeds.cpp:1008:44: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
/builds/precommit_linux64/opencv/modules/imgproc/src/seeds.cpp:1009:44: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
/builds/precommit_linux64/opencv/modules/imgproc/src/seeds.cpp:1011:50: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
/builds/precommit_linux64/opencv/modules/imgproc/src/seeds.cpp:1012:46: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
/builds/precommit_linux64/opencv/modules/imgproc/src/seeds.cpp:1013:50: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
/builds/precommit_linux64/opencv/modules/imgproc/src/seeds.cpp:1014:50: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
/builds/precommit_linux64/opencv/modules/imgproc/src/seeds.cpp:1059:50: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
/builds/precommit_linux64/opencv/modules/imgproc/src/seeds.cpp:1060:46: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
/builds/precommit_linux64/opencv/modules/imgproc/src/seeds.cpp:1061:50: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
/builds/precommit_linux64/opencv/modules/imgproc/src/seeds.cpp:1063:44: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
/builds/precommit_linux64/opencv/modules/imgproc/src/seeds.cpp:1064:44: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
/builds/precommit_linux64/opencv/modules/imgproc/src/seeds.cpp:1066:50: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
/builds/precommit_linux64/opencv/modules/imgproc/src/seeds.cpp:1067:50: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
/builds/precommit_linux64/opencv/modules/imgproc/src/seeds.cpp:1069:50: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
/builds/precommit_linux64/opencv/modules/imgproc/src/seeds.cpp:1070:46: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
/builds/precommit_linux64/opencv/modules/imgproc/src/seeds.cpp:1071:50: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]

    12>C:\builds_ocv\precommit_windows64\opencv\modules\imgproc\src\seeds.cpp(201): warning C4146: unary minus operator applied to unsigned type, result still unsigned [C:\builds_ocv\precommit_windows64\build\modules\imgproc\opencv_imgproc.vcxproj]

    12>C:\builds_ocv\precommit_windows64\opencv\modules\imgproc\src\seeds.cpp(220): warning C4305: 'argument' : truncation from 'double' to 'float' [C:\builds_ocv\precommit_windows64\build\modules\imgproc\opencv_imgproc.vcxproj]

    12>C:\builds_ocv\precommit_windows64\opencv\modules\imgproc\src\seeds.cpp(268): warning C4244: 'initializing' : conversion from 'double' to 'int', possible loss of data [C:\builds_ocv\precommit_windows64\build\modules\imgproc\opencv_imgproc.vcxproj]

    12>C:\builds_ocv\precommit_windows64\opencv\modules\imgproc\src\seeds.cpp(278): warning C4244: 'initializing' : conversion from 'float' to 'int', possible loss of data [C:\builds_ocv\precommit_windows64\build\modules\imgproc\opencv_imgproc.vcxproj]

    12>C:\builds_ocv\precommit_windows64\opencv\modules\imgproc\src\seeds.cpp(279): warning C4244: 'initializing' : conversion from 'float' to 'int', possible loss of data [C:\builds_ocv\precommit_windows64\build\modules\imgproc\opencv_imgproc.vcxproj]

    12>C:\builds_ocv\precommit_windows64\opencv\modules\imgproc\src\seeds.cpp(293): warning C4244: 'initializing' : conversion from 'double' to 'int', possible loss of data [C:\builds_ocv\precommit_windows64\build\modules\imgproc\opencv_imgproc.vcxproj]

    12>C:\builds_ocv\precommit_windows64\opencv\modules\imgproc\src\seeds.cpp(294): warning C4244: 'initializing' : conversion from 'double' to 'int', possible loss of data [C:\builds_ocv\precommit_windows64\build\modules\imgproc\opencv_imgproc.vcxproj]

    12>C:\builds_ocv\precommit_windows64\opencv\modules\imgproc\src\seeds.cpp(1229): warning C4245: '=' : conversion from 'int' to 'uchar', signed/unsigned mismatch [C:\builds_ocv\precommit_windows64\build\modules\imgproc\opencv_imgproc.vcxproj]