Avoiding a possible crash in AudioUnits.

modules/juce_audio_processors/format_types/juce_AudioUnitPluginFormat.mm

@@ -523,14 +523,16 @@ public:
 
             for (int i = 0; i < numOutputBusses; ++i)
             {
-                AudioBufferList* const abl = getAudioBufferListForBus(i);
-                abl->mNumberBuffers = numOutputBusChannels;
-
-                for (int j = 0; j < numOutputBusChannels; ++j)
+                if (AudioBufferList* const abl = getAudioBufferListForBus(i))
                 {
-                    abl->mBuffers[j].mNumberChannels = 1;
-                    abl->mBuffers[j].mDataByteSize = sizeof (float) * numSamples;
-                    abl->mBuffers[j].mData = buffer.getWritePointer (i * numOutputBusChannels + j);
+                    abl->mNumberBuffers = numOutputBusChannels;
+
+                    for (int j = 0; j < numOutputBusChannels; ++j)
+                    {
+                        abl->mBuffers[j].mNumberChannels = 1;
+                        abl->mBuffers[j].mDataByteSize = sizeof (float) * numSamples;
+                        abl->mBuffers[j].mData = buffer.getWritePointer (i * numOutputBusChannels + j);
+                    }
                 }
             }