fix window size changes during some message interactions

After a call, a signal wasn't disconnected properly. This was leading
to resizings for no apparent reason when receiving or sending a
message after this was ended.

This was caused by the in-call chat window, invisible at this time, to
be opened because of that signal. We now disconnect it when closing
call view.

Change-Id: Icd211bad795e146353e099004c1ba13eadccf9ba
Reviewed-by: Olivier Soldano <olivier.soldano@savoirfairelinux.com>

src/CurrentCallVC.mm

@@ -563,6 +563,7 @@
     QObject::disconnect(previewHolder.frameUpdated);
     QObject::disconnect(previewHolder.stopped);
     QObject::disconnect(previewHolder.started);
+    QObject::disconnect(self.messageConnection);
     [previewView.layer setContents:nil];
 
     [_brokerPopoverVC performClose:self];