JUCE/VST2: Prevent crash of effGetSpeakerArrangement with null in/out

Adobe Premier 2023 when scanning for VST2 plugins calls
Vst2::effGetSpeakerArrangement with pointer to null in/out speaker
arrangement.

Not sure if it valid to do for the host, but we have to adapt
regardless.

See: werman#154
JUCE issue: juce-framework/JUCE#1167

Author: werman

external/JUCE/modules/juce_audio_plugin_client/VST/juce_VST_Wrapper.cpp

@@ -1972,7 +1972,7 @@ class JuceVSTWrapper  : public AudioProcessorListener,
         auto** pluginInput  = reinterpret_cast<Vst2::VstSpeakerArrangement**> (args.value);
         auto** pluginOutput = reinterpret_cast<Vst2::VstSpeakerArrangement**> (args.ptr);
 
-        if (pluginHasSidechainsOrAuxs() || processor->isMidiEffect())
+        if (pluginHasSidechainsOrAuxs() || processor->isMidiEffect() || !*pluginInput || !*pluginOutput)
             return false;
 
         auto inputLayout  = processor->getChannelLayoutOfBus (true,  0);