AU Host: Improve allocation checks

If the block size changes from block to block, then it's possible for
inputBuffer to be smaller than buffer, but for buffer to be smaller than
the initially-allocated size of inputBuffer.

modules/juce_audio_processors/format_types/juce_AudioUnitPluginFormat.mm

@@ -1101,8 +1101,9 @@ public:
             inMapping .setUpMapping (audioUnit, true);
             outMapping.setUpMapping (audioUnit, false);
 
-            inputBuffer.setSize (jmax (getTotalNumInputChannels(), getTotalNumOutputChannels()),
-                                 estimatedSamplesPerBlock);
+            preparedChannels = jmax (getTotalNumInputChannels(), getTotalNumOutputChannels());
+            preparedSamples  = estimatedSamplesPerBlock;
+            inputBuffer.setSize (preparedChannels, preparedSamples);
         }
     }
 
@@ -1130,8 +1131,8 @@ public:
     void processAudio (AudioBuffer<float>& buffer, MidiBuffer& midiMessages, bool processBlockBypassedCalled)
     {
         // If these are hit, we might allocate in the process block!
-        jassert (buffer.getNumChannels() <= inputBuffer.getNumChannels());
-        jassert (buffer.getNumSamples()  <= inputBuffer.getNumSamples());
+        jassert (buffer.getNumChannels() <= preparedChannels);
+        jassert (buffer.getNumSamples()  <= preparedSamples);
         // Copy the input buffer to guard against the case where a bus has more output channels
         // than input channels, so rendering the output for that bus might stamp over the input
         // to the following bus.
@@ -1724,7 +1725,7 @@ private:
     AudioBuffer<float> inputBuffer;
     Array<Array<AudioChannelSet>> supportedInLayouts, supportedOutLayouts;
 
-    int numChannelInfos;
+    int numChannelInfos, preparedChannels = 0, preparedSamples = 0;
     HeapBlock<AUChannelInfo> channelInfos;
 
     AudioUnit audioUnit;