fix: unblock main thread after mutex unlock in DeferredDeleter

DeferredDeleter instance could get deleted before worker thread called
unlock() on queue mutex leading to an error

Related-To: NEO-14896

Signed-off-by: Oskar Hubert Weber <oskar.hubert.weber@intel.com>

shared/source/memory_manager/deferred_deleter.cpp

@@ -107,8 +107,8 @@ void *DeferredDeleter::run(void *arg) {
         lock.lock();
         // Check whether working thread should be stopped
     } while (!self->shouldStop());
-    self->exitedMainLoop = true;
     lock.unlock();
+    self->exitedMainLoop = true;
     return nullptr;
 }