[core] Graph: avoid double update while adding/removing an edge

Graph.markNodesDirty() is called in three different places:
- Attribute.requestGraphUpdate()
- Graph.addEdge()
- Graph.removeEdge()

However, addEdge() and removeEdge() are especially decorated to request a graph update so, with the old markNodesDirty() implementation, the update was done twice in a row.

meshroom/core/attribute.py

@@ -142,6 +142,7 @@ class Attribute(BaseObject):
     def requestGraphUpdate(self):
         if self.node.graph:
             self.node.graph.markNodesDirty(self.node)
+            self.node.graph.update()
 
     @property
     def isOutput(self):