Bugs in gif.c

[laoliangyouqu]

The processing of the extension in gif.c has following bugs:

(1) It displace the comment extension for animated Gif, i.e., it puts the comment extension of ith frame to (i-1)th frame, and drops the comment extension of 0th frame.

(2) It only saves at most one comment extension per frame (Gif specification has no such limit) -- SetImageProperty(image,"comment",comments) overwrites the previous comment.

(3) It drops the text extension automatically -- the text extension is processed through "default" path and is dropped.

[magick]

ImageMagick currently only supports one comment per image. We'll investigate supporting multiple comments.

Do you have an example image we can download with a text extension? We'll use it to come up with a patch for this problem.

We'll have a fix for the off by one comment problem within a day or two.