Add possible workaround for model invalidate().

qutebrowser/utils/completion.py

@@ -314,10 +314,7 @@ class CompletionFilterModel(QSortFilterProxyModel):
                 srcmodel.sort(sortcol)
             except NotImplementedError:
                 self.sort(sortcol)
-            # FIXME  we should call self.invalidate() here so sorting actually works.
-            # However, this seems to provoke a lot of weird problems, like
-            # random race condition segfaults :(
-            # self.invalidate()
+            self.invalidate()
 
     def filterAcceptsRow(self, row, parent):
         """Custom filter implementation.

qutebrowser/widgets/completion.py

@@ -80,6 +80,12 @@ class CompletionView(QTreeView):
         self.setHeaderHidden(True)
         self.setIndentation(0)
         self.setItemsExpandable(False)
+        # FIXME This is a workaround for weird race conditions with invalid
+        # item indexes leading to segfaults in Qt.
+        #
+        # Some background: http://bugs.quassel-irc.org/issues/663
+        # The proposed fix there was later reverted because it didn't help.
+        self.setUniformRowHeights(True)
         self.hide()
         # FIXME set elidemode