Replacing tweak key-map items with click-drag caused selection
in the graph/sequencer/node editors to ignore drag events
(all uses of WM_generic_select_modal).
Operators that return OPERATOR_PASS_THROUGH | OPERATOR_FINISHED
result in the event loop considering the event as being handled.
This stopped WM_CLICK_DRAG events from being generated which is not the
case for tweak events.
As click-drag is intended to be compatible with tweak events,
accept drag events when WM_HANDLER_BREAK isn't set or when
wm_action_not_handled returns true.
cf428b2ebd