Make sure JNI_OnLoad is not called more than once

Since Android 5.0 Google introduce a nasty bug[1] which calls
JNI_OnLoad more than once.
Basically every time when a library is loaded JNI_OnLoad is
called if found, but it calls *again* JNI_OnLoad of its .so
dependencies!

[1] Workaround https://code.google.com/p/android/issues/detail?id=215069

Change-Id: I81b4a94beedaad299267ac6deab2f9c3a1693a62
Reviewed-by: Eskil Abrahamsen Blomfeldt <eskil.abrahamsen-blomfeldt@qt.io>

src/plugins/android/src/qandroidmediaserviceplugin.cpp

@@ -145,6 +145,11 @@ QT_END_NAMESPACE
 #ifndef Q_OS_ANDROID_NO_SDK
 Q_DECL_EXPORT jint JNICALL JNI_OnLoad(JavaVM *vm, void * /*reserved*/)
 {
+    static bool initialized = false;
+    if (initialized)
+        return JNI_VERSION_1_6;
+    initialized = true;
+
     QT_USE_NAMESPACE
     typedef union {
         JNIEnv *nativeEnvironment;