Crash on certain hosts due to initial preset value being set to -1

[yamadapc]

This is fine on most iOS hosts, but for AUM (https://apps.apple.com/us/app/aum-audio-mixer/id1055636344) which is a highly used host for iOS, the fact the initial program is set to -1 causes the plugin to crash.

The reason is that -1 is not a valid program index and JUCE AudioUnit code is not handling -1 as an input. See:

• juce::JuceAudioUnitv3::FactoryPresets::getAtIndex

What AUM seems to do it:

• Create the plugin filter; here the RNBO::JuceAudioProcessor constructor sets the current program to -1
• Get the current preset by calling juce::JuceAudioUnitv3::getCurrentPreset

AUAudioUnitPreset* getCurrentPreset() const
{
    return factoryPresets.getAtIndex (getAudioProcessor().getCurrentProgram());
}

• At this point, we're calling factoryPresets.getAtIndex (-1); see the implementation of this method does no lower bounds checking

AUAudioUnitPreset* getAtIndex (int index) const
{
     std::lock_guard<std::mutex> lock (mutex);

     if (index < (int) [presets.get() count])
          return [presets.get() objectAtIndex: (unsigned int) index];

     return nullptr;
}

• The plugin crashes due to objectAtIndex trying to access index - 1 of that array

The fix could be to for RNBO::JuceAudioProcessor's _currentPresetIdx field to be initialised to 0 or a different value. I can verify setting the program to 0 (as well as patching JUCE bounds checking code above to consider lower bounds) fixes crashes in AUM for my iOS plugin.

All the best

[yamadapc]

The problem is on RNBO_JuceAudioProcessors.cpp line 246:

	, _currentPresetIdx(-1)

[yamadapc]

Closing this in favour of Cycling74/rnbo.adapter.juce#5