Gets "list Index out of range" when loading image

[mriale]

Crashes program when using drag and drop to load an image with less colors than the current image.

Steps to recreate:

• Drag and drop this file into PyDPainter: iff_pics/fish.iff
• In the palette, click the right arrow to go to the next page page of colors
• Drag and drop this file into PyDPainter: iff_pics/fire.iff
• Crash closes PyDPainter