Blender Git Loki

Fix tooltip disabled hint not using correct context from the button

To display the "disabled hint" (text explaining why a button is disabled) in a
tooltip, it would run the operator poll callback, which could then set a poll
message. But the context for the poll check wasn't the one from the button, so
the poll may give a different result (and disabled hint) than the check of the
button itself did.
Make sure it uses the exact context from the button.