Fix potential crash caused by internal GM synth

Author: timothyschoen

Source/Standalone/InternalSynth.cpp

@@ -168,7 +168,8 @@ void InternalSynth::process(AudioBuffer<float>& buffer, MidiBuffer& midiMessages
     // Run audio through fluidsynth
     fluid_synth_process(synth, buffer.getNumSamples(), std::max(2, buffer.getNumChannels()), const_cast<float**>(internalBuffer.getArrayOfReadPointers()), std::max(2, buffer.getNumChannels()), const_cast<float**>(internalBuffer.getArrayOfWritePointers()));
 
-    for (int ch = 0; ch < buffer.getNumChannels(); ch++) {
+    int numChannelsToProcess = std::min(buffer.getNumChannels(), internalBuffer.getNumChannels());
+    for (int ch = 0; ch < numChannelsToProcess; ch++) {
         buffer.addFrom(ch, 0, internalBuffer, ch, 0, buffer.getNumSamples());
     }