fixup! EditScopePlugValueWidget : Filter available nodes using Contex…

…tTracker

python/GafferUI/EditScopeUI.py

@@ -211,7 +211,6 @@ def __plugInputChanged( self, plug ) :
 		if plug.getName() == "in" and plug.parent() == self.getPlug().node() :
 			# The result of `__inputNode()` will have changed.
 			self.__acquireContextTracker()
-			self.__updateMenuButton()
 
 	def __acquireContextTracker( self ) :
 
@@ -220,6 +219,12 @@ def __acquireContextTracker( self ) :
 			Gaffer.WeakMethod( self.__contextTrackerChanged ), scoped = True
 		)
 
+		if not self.__contextTracker.updatePending() :
+			self.__updateMenuButton()
+		else :
+			# We'll update later in `__contextTrackerChanged()`.
+			pass
+
 	def __updateMenuButton( self ) :
 
 		editScope = self.__editScope()