Resize completion when it's shown, and only then.

Before this, we always resized the completion when the mainwindow was resized.
If the statusbar is hidden during the resize (ui -> hide-statusbar is true), we
got an invalid calculated QRect for the completion, causing the update to be
not applied at all - so the completion showed up incorrectly.

With this change, another resize is done when the completion is shown - at this
point it's certain the statusbar is visible. Also we only update it while it's
shown - it doesn't make sense to always adjust its size when it's hidden
anyways.

qutebrowser/completion/completionwidget.py

@@ -241,3 +241,8 @@ class CompletionView(QTreeView):
         """Extend resizeEvent to adjust column size."""
         super().resizeEvent(e)
         self._resize_columns()
+
+    def showEvent(self, e):
+        """Adjust the completion size when it's freshly shown."""
+        self.resize_completion.emit()
+        super().showEvent(e)

qutebrowser/mainwindow/mainwindow.py

@@ -266,6 +266,10 @@ class MainWindow(QWidget):
     @pyqtSlot()
     def resize_completion(self):
         """Adjust completion according to config."""
+        if not self._completion.isVisible():
+            # It doesn't make sense to resize the completion as long as it's
+            # not shown anyways.
+            return
         # Get the configured height/percentage.
         confheight = str(config.get('completion', 'height'))
         if confheight.endswith('%'):