Fix segfault when removing displays

When there was an instance of a DisplayGroupVisibilityProperty (e.g. due to a CameraDisplay),
the display's virtual function BoolProperty::getBool() was called from the Property destructor
(when removing it from the model), which caused undefined behavior.

Author: rhaschke

src/rviz/displays_panel.cpp

@@ -179,6 +179,8 @@ void DisplaysPanel::onDeleteDisplay()
     // Displays can emit signals from other threads with self pointers.  We're
     // freeing the display now, so ensure no one is listening to those signals.
     displays_to_delete[ i ]->disconnect();
+    // Remove dipslay from property tree to avoid memory access after deletion
+    displays_to_delete[ i ]->getParent()->takeChild(displays_to_delete[ i ]);
     // Delete display later in case there are pending signals to it.
     displays_to_delete[ i ]->deleteLater();
   }