QUICKFLI: fix crash due to bad refactoring.

Fixes commit 91ddac838d8ea6a64b7f212f2db7423b012322db.
Fix a bug with the indices in cset_colors.
Use memmove for copy_bytes/copy_words as src/dst may overlap.
PLAY: clip source dimensions when saving the buffer under the mouse.
Merge pull request #10 from wangds/master

Bug fixes.