KMLSuperOverlay: remove useless and unreliable computations on floating point numbers that caused issues (truncated raster) on 32bit (#5683)

git-svn-id: https://svn.osgeo.org/gdal/trunk@27809 f0d54148-0727-0410-94bb-9a71ac55c965
Merge branch 'trunk' into trunk_travis_macosx