Fixed some indentation in coders/png.c and added some whitespace.
Fixed some indentation in coders/png.c and added some whitespace.


UniQP/ImageMagick,UniQP/ImageMagick,kwm81/ImageMagick,UniQP/ImageMagick,UniQP/ImageMagick,kwm81/ImageMagick,kwm81/ImageMagick,Danack/ImageMagick,Danack/ImageMagick,kwm81/ImageMagick,UniQP/ImageMagick,kwm81/ImageMagick,Danack/ImageMagick,Danack/ImageMagick,Danack/ImageMagick,kwm81/ImageMagick,UniQP/ImageMagick,Danack/ImageMagick