[libpng14] Revised png_check_IHDR() to use PNG_SIZE_MAX instead of

PNG_UINT_32_MAX in the test for potential overflow in PNG_ROWBYTES.
[libpng14] Removed potentially misleading warning from png_check_IHDR().
 [libpng14] Imported from libpng-1.4.13beta05.tar
[libpng14] Bump version to 1.4.13beta06