android: deadlock when Emulator::checkStatus is called concurrently

If checkStatus(wait = true) is called, any other thread will be blocked
even when calling with wait = false since the mutex is locked. This
happens on Android when JNIdc.rendinitNative(null) is called by the app
main thread.
Use a shared_future instead and unlock the mutex before waiting.

core/emulator.cpp

@@ -908,15 +908,20 @@ void Emulator::start()
 bool Emulator::checkStatus(bool wait)
 {
 	try {
-		const std::lock_guard<std::mutex> lock(mutex);
+		std::unique_lock<std::mutex> lock(mutex);
 		if (threadResult.valid())
 		{
-			if (!wait)
-			{
-				auto result = threadResult.wait_for(std::chrono::seconds(0));
+			lock.unlock();
+			auto localResult = threadResult;
+			if (wait) {
+				localResult.wait();
+			}
+			else {
+				auto result = localResult.wait_for(std::chrono::seconds(0));
 				if (result == std::future_status::timeout)
 					return true;
 			}
+			lock.lock();
 			threadResult.get();
 		}
 		return false;

core/emulator.h

@@ -179,7 +179,7 @@ private:
 		Terminated,
 	};
 	State state = Uninitialized;
-	std::future<void> threadResult;
+	std::shared_future<void> threadResult;
 	bool resetRequested = false;
 	bool singleStep = false;
 	u64 startTime = 0;