Describe your bug report or feature request here

Basically, when you enable symmetry, sometimes (?) the paint-bucket tool goes "through" the pixels and fills in the background. Sometimes it also fills in non-transparent pixel clusters, as well. Here's a video that shows the issue better.

Aseprite and System version

• Aseprite: Version 1.1.7, installed from .deb
• System: Linux, Ubuntu Gnome, 16.04:

Here's the example .ase file, as well. To reproduce the issue, enable vertical symmetry, and then try to fill the dark red pixels toward the outer edges of the "scarf".