Stop searching for timeout once identifier found

The identifier is unique.

Use QList::contains() rather than a nested for loop; break from the
QHash loop once the search succeeds.

Continuing to loop over the action timeouts should be safe but the
brightness action may use KAuth which may return to the event loop; this
allows another event to e.g. call loadProfile() which will reload all
actions and kick over the timeouts.

CCBUG: 315379
REVIEW: 110026