Fix contiguous selection tool working on projection

Before this commit, the tool tried to access paint device of the layer
and return if there was none (which is the case for group layers).
This commit changes it to look for projection() instead, as it was
before the color labeled layers patch.

Using the paind device seemed to cause two bugs. It wasn't working on
group layers and clicking outside of the canvas didn't deselect.

BUG:423336
BUG:423237

(cherry picked from commit 96e3af27f78e0b02341b71351b5aba19ade486a9)