[dbmanager] skip RuntimeError: fixes #6892

Author: slarosa

python/plugins/db_manager/layer_preview.py

@@ -74,7 +74,11 @@ def setDirty(self, val=True):
   def _clear(self):
     """ remove any layers from preview canvas """
     if self.item is not None:
-      self.disconnect(self.item, SIGNAL('aboutToChange'), self.setDirty)
+      ## skip exception on RuntimeError fixes #6892
+      try:
+        self.disconnect(self.item, SIGNAL('aboutToChange'), self.setDirty) 
+      except RuntimeError:
+        pass
     self.item = None
     self.dirty = False