AU plugin factory class fix.

modules/juce_audio_plugin_client/AU/juce_AU_Wrapper.mm

@@ -1439,11 +1439,17 @@ private:
         return ComponentEntryPoint<Class>::Dispatch (params, obj); \
     }
 
+#if JucePlugin_ProducesMidiOutput || JucePlugin_WantsMidiInput
+ #define FACTORY_BASE_CLASS AUMIDIEffectFactory
+#else
+ #define FACTORY_BASE_CLASS AUBaseFactory
+#endif
+
 #define JUCE_FACTORY_ENTRYX(Class, Name) \
     extern "C" __attribute__((visibility("default"))) void* Name ## Factory (const AudioComponentDescription* desc); \
     extern "C" __attribute__((visibility("default"))) void* Name ## Factory (const AudioComponentDescription* desc) \
     { \
-        return AUBaseFactory<Class>::Factory (desc); \
+        return FACTORY_BASE_CLASS<Class>::Factory (desc); \
     }
 
 #define JUCE_COMPONENT_ENTRY(Class, Name, Suffix)   JUCE_COMPONENT_ENTRYX(Class, Name, Suffix)