libpng: Integer overflow and resultant divide-by-zero in pngrutil.c:png_check_chunk_length() allows for denial of service

In libpng 1.6.34, a wrong calculation of rowfactor in the pngcheckchunklength function pngrutil.c may trigger an integer overflow and resultant divide-by-zero while processing a crafted PNG file, leading to a denial of service...