Restore back condition to set current history in backend

The effect of this is that we can switch to any owned history in the UI, but if the history has been deleted it will not change the current history in the backend and a browser refresh will bring back the real current history.

lib/galaxy/webapps/base/webapp.py

@@ -914,7 +914,7 @@ def get_history(self, create=False, most_recent=False):
         return history
 
     def set_history(self, history):
-        if history:
+        if history and not history.deleted:
             self.galaxy_session.current_history = history
         self.sa_session.add(self.galaxy_session)
         with transaction(self.sa_session):
@@ -932,7 +932,7 @@ def get_or_create_default_history(self):
 
         # Just return the current history if one exists and is not deleted.
         history = self.galaxy_session.current_history
-        if history:
+        if history and not history.deleted:
             return history
 
         # Look for an existing history that has the default name, is not