UI: meaningful error for tree update fail

this commit invalidates the tree hash on parse fail,
so that the error message is created by the popup
and sent to the user, and so the user doesn't have to
force update the tree.

these sorts of errors should be rare

base_definitions.py

@@ -126,9 +126,10 @@ class MantisTree(NodeTree):
                 if context:
                     self.display_update(context)
                 self.tree_valid = True
-            except GraphError as e:
+            except Exception as e:
                 prRed("Failed to update node tree due to error.")
                 self.tree_valid = False
+                self.hash='' # unset the hash to mark the tree as un-parsed.
                 raise e
             finally:
                 scene.render.use_lock_interface = False