AnimationEditor : Fix changing of frame by click & drag

We mustn't edit the context returned by the ContextTracker - nobody is tracking it for changes, it is intended to be const, and other UI components might be using it in other threads. Instead we just use the ScriptNode context in the AnimationEditor as before.

This is the most minimal change needed to fix the bug. You could argue the case for making the AnimationEditor genuinely focus-aware by accounting for TimeWarps between the node being viewed and the node being edited. That would require a lot of work though, and it's not clear that it's worth it, or that it can be done without an ABI break.

Changes.md

@@ -15,6 +15,7 @@ Fixes
 - Render, InteractiveRender : Added default node name arguments to the compatibility shims for removed subclasses such as ArnoldRender.
 - GafferUITest : Fixed `assertNodeUIsHaveExpectedLifetime()` test for invisible nodes.
 - OpDialogue : Fixed `postExecuteBehaviour` handling.
+- AnimationEditor : Fixed changing of the current frame by dragging the frame indicator or clicking on the time axis.
 
 API
 ---

python/GafferUI/AnimationEditor.py

@@ -150,6 +150,7 @@ def __init__( self, scriptNode, **kw ) :
 
 		# Set up the widget responsible for actual curve drawing
 		self.__animationGadget = GafferUI.AnimationGadget()
+		self.__animationGadget.setContext( scriptNode.context() )
 
 		# Set up signals needed to update selection state in PathListingWidget
 		editable = self.__animationGadget.editablePlugs()
@@ -222,10 +223,6 @@ def _updateFromSet( self ) :
 		self.__pathChangedConnection = self.__curveList.getPath().pathChangedSignal().connect( Gaffer.WeakMethod( self.__updateGadgetSets ), scoped = True )
 		self.__updateGadgetSets()
 
-	def _updateFromContext( self, modifiedItems ) :
-
-		self.__animationGadget.setContext( self.context() )
-
 	def __updateGadgetSets( self, unused = None ) :
 
 		visiblePlugs = set()