ScenePathPlugValueWidget : Fix bug finding scene for promoted plug
ScenePathPlugValueWidget : Fix bug finding scene for promoted plug

If a plug has been promoted but no corresponding ScenePlug has been too, we consider all plug outputs to try to find a ScenePlug on the node the plug was promoted from.

ImageEngine/gaffer,boberfly/gaffer,lucienfostier/gaffer,GafferHQ/gaffer,johnhaddon/gaffer,lucienfostier/gaffer,ImageEngine/gaffer,andrewkaufman/gaffer,boberfly/gaffer,hradec/gaffer,andrewkaufman/gaffer,johnhaddon/gaffer,johnhaddon/gaffer,appleseedhq/gaffer,hradec/gaffer,hradec/gaffer,appleseedhq/gaffer,ImageEngine/gaffer,andrewkaufman/gaffer,GafferHQ/gaffer,ImageEngine/gaffer,johnhaddon/gaffer,boberfly/gaffer,lucienfostier/gaffer,hradec/gaffer,GafferHQ/gaffer,hradec/gaffer,andrewkaufman/gaffer,boberfly/gaffer,GafferHQ/gaffer,appleseedhq/gaffer,appleseedhq/gaffer,GafferHQ/gaffer,andrewkaufman/gaffer,lucienfostier/gaffer,johnhaddon/gaffer