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! So, JNI_OnLoad of libQt5Core.so gets called may times,
this is not a problem as long as it's called from Qt's java delegate
class loader. The problem is that the application .so file *must* be
called from default class loader to allow the user to find his custom
Activity/Service stuff.


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

Change-Id: Ia71209658ef56056b560018597608acf7cb0f9ea
Reviewed-by: Eskil Abrahamsen Blomfeldt <eskil.abrahamsen-blomfeldt@qt.io>

src/corelib/kernel/qjnionload.cpp

@@ -38,6 +38,11 @@ Q_CORE_EXPORT jint JNICALL JNI_OnLoad(JavaVM *vm, void *reserved)
 {
     Q_UNUSED(reserved)
 
+    static bool initialized = false;
+    if (initialized)
+        return JNI_VERSION_1_6;
+    initialized = true;
+
     typedef union {
         JNIEnv *nenv;
         void *venv;

src/plugins/platforms/android/androidjnimain.cpp

@@ -822,6 +822,11 @@ QT_END_NAMESPACE
 
 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;