video_source.h,ReallocImage: quiet implicit conv warning
video_source.h,ReallocImage: quiet implicit conv warning

with -fsanitize=undefined

test/video_source.h:194:33: runtime error: implicit conversion from type
'int' of value -32 (32-bit, signed) to type 'unsigned int' changed the
value to 4294967264 (32-bit, unsigned)

Change-Id: I92013086d517fecf01c9e4cdfe6737b8ce733a1f

webmproject/libvpx,ShiftMediaProject/libvpx,webmproject/libvpx,webmproject/libvpx,webmproject/libvpx,ShiftMediaProject/libvpx,webmproject/libvpx,webmproject/libvpx,ShiftMediaProject/libvpx,ShiftMediaProject/libvpx,ShiftMediaProject/libvpx