[qt-android] Crash when JNI is called from multipile threads

I have a qt5 android program which will call JNI code in multiple threads, it will randomly crashed, I found it crashed in getCachedMethodID() in qjni.cpp through core dump.
It seems that getCachedMethodID() will access a global data structure JMethodIDHash, and it is totally un-protected from multi-threaded access. I think we should use a mutex to protect it.