Moving the cursor away from the extensions "Add Repository" popup
could crash because the "Repositories" popover was closed while the
popup it created remains open.
Resolve by clearing wmEventHandler_UI::context.region_popup
which match the freed region, following similar logic already used by
WM_event_modal_handler_region_replace.
Note that this bug was exposed by [0].
[0]: 38d11482f5