hotfix: release mutex via activeThreadGuard pointer, not the optional one (threadGuard instead of dummyGuard for crypto thread) (#8414)

Co-authored-by: aleksey.mochalov <[email protected]>

Author: MochalovAlexey

src/jrd/jrd.cpp

@@ -6476,7 +6476,7 @@ static void release_attachment(thread_db* tdbb, Jrd::Attachment* attachment)
 		}
 
 		// Notify special threads
-		threadGuard.leave();
+		activeThreadGuard->leave();
 
 		// Sync with special threads
 		sync.unlock();