Fix issue #8548 on gajim_0.16: Do not close chat window on ESC key when roster filtering is active
When the roster window active it can be filtered by starting to type. If the window behavior "single window for everything" is selected, trying to abort the filtering by pressing the ESC key also closes a chat window. Fix this behavior by stopping event propagation in case the ESC key is pressed while roster filtering is active.
Fixes issue #8548 (closed).