Removed unused variable "skip_to_iend" from coders/png.c
Removed unused variable "skip_to_iend" from coders/png.c


git-svn-id: 7f11a4e55de7d4642c7675696f15857479c93c9d@15973 aa41f4f7-0bf4-0310-aa73-e5a19afd5a74

svn2github/ImageMagick,svn2github/ImageMagick,svn2github/ImageMagick,svn2github/ImageMagick