MultiLineTextWidget : Avoid linear-time signal methods

We don't care exactly how many slots are connected, just if _any_ slot is connected. The latter is achievable in constant time while the former is linear in the number of slots.

python/GafferUI/MultiLineTextWidget.py

@@ -506,7 +506,7 @@ def __paintActivationHint( self, painter ) :
 			return
 
 		widget = GafferUI.Widget._owner( self )
-		if widget is None or ( widget.activatedSignal().numSlots() + widget.editingFinishedSignal().numSlots() ) == 0 :
+		if widget is None or ( widget.activatedSignal().empty() and widget.editingFinishedSignal().empty() ) :
 			return
 
 		viewport = self.viewport()