Receiving a new message causes the topic editor to deselect and lose changes
I'm using quassel v0.13-pre (0.12.0+690 git-cb63e88d)
The core uses 1:0.13.0~alpha+201806212016-0ubuntu0~built201806220131~gitda1a6f4~ubuntu18.04.1
qtui: Keep editing topic while someone talks
Without this change, it's almost impossible to edit the topic with the
topic widget in busy channels because every message would trigger the
dataChanged signal which would reset the topic and switch the topic
widget out of editing mode.