Fix hang on stop before run w/ multithreading.

And clarify logic.

Core/ThreadEventQueue.h

@@ -112,6 +112,22 @@ struct ThreadEventQueue : public B {
 		eventsHaveRun_ = false;
 	}
 
+	inline bool ShouldSyncThread(bool force) {
+		if (!HasEvents())
+			return false;
+		if (coreState != CORE_RUNNING && !force)
+			return false;
+
+		// Don't run if it's not running, but wait for startup.
+		if (!eventsRunning_) {
+			if (eventsHaveRun_ || coreState == CORE_ERROR || coreState == CORE_POWERDOWN) {
+				return false;
+			}
+		}
+
+		return true;
+	}
+
 	// Force ignores coreState.
 	void SyncThread(bool force = false) {
 		if (!threadEnabled_) {
@@ -122,7 +138,7 @@ struct ThreadEventQueue : public B {
 		// While processing the last event, HasEvents() will be false even while not done.
 		// So we schedule a nothing event and wait for that to finish.
 		ScheduleEvent(EVENT_SYNC);
-		while (HasEvents() && (eventsRunning_ || !eventsHaveRun_) && (force || coreState == CORE_RUNNING)) {
+		while (ShouldSyncThread(force)) {
 			eventsDrain_.wait(eventsLock_);
 		}
 	}