Fix tautologies in calibfilter.cpp which cause a build failure when using -Werror=address with clang-3.5

http://code.opencv.org/issues/4048

calibfilter.cpp:98:9: error: comparison of array 'this->latestPoints' not equal to a null pointer is always true [-Werror,-Wtautological-pointer-compare]
if (latestPoints != __null)
^~~~~~~~~~ ~~~~

calibfilter.cpp:526:9: error: address of array 'this->latestCounts' will always evaluate to 'true' [-Werror,-Wpointer-bool-conversion]
if( latestCounts )
~ ^~~~~~~~~~~
2 errors generated.

Signed-off-by: Jeremy Huddleston Sequoia <jeremyhu@apple.com>