android: race condition on Emulator::threadResult

The emu thread can be stopped/started by the app main java thread while
the render thread is running. This can lead to a race condition on the
threadResult future between checkStatus() and start(). So protect
relevant sections with a mutex.

Fix for MINIDUMP-1G, MINIDUMP-1H, MINIDUMP-2G and MINIDUMP-33

core/emulator.cpp

@@ -847,6 +847,7 @@ void Emulator::start()
 
 	if (config::ThreadedRendering)
 	{
+		const std::lock_guard<std::mutex> lock(mutex);
 		threadResult = std::async(std::launch::async, [this] {
 				InitAudio();
 
@@ -881,6 +882,7 @@ void Emulator::start()
 bool Emulator::checkStatus()
 {
 	try {
+		const std::lock_guard<std::mutex> lock(mutex);
 		if (threadResult.valid())
 		{
 			auto result = threadResult.wait_for(std::chrono::seconds(0));

core/emulator.h

@@ -27,6 +27,7 @@
 #include <string>
 #include <memory>
 #include <utility>
+#include <mutex>
 
 void loadGameSpecificSettings();
 void SaveSettings();
@@ -178,6 +179,7 @@ private:
 	u32 stepRangeFrom = 0;
 	u32 stepRangeTo = 0;
 	bool stopRequested = false;
+	std::mutex mutex;
 };
 extern Emulator emu;