FX Mode handles block mod buffers better

In the event we are in non-latent mode and our buffer is
not a multiple of block size, then

1: reset the inputs and outputs
2: Enter latent mode
3: set latency and
4: inform the host of a latency change

Addresses surge-synthesizer#6638 but some testing before we close it would be
super.

src/surge-fx/SurgeFXProcessor.cpp

@@ -186,6 +186,20 @@ void SurgefxAudioProcessor::processBlock(juce::AudioBuffer<float> &buffer,
         resetFxParams(true);
     }
 
+    auto sampl = buffer.getNumSamples();
+    if (nonLatentBlockMode && ((sampl & ~(BLOCK_SIZE-1)) != sampl))
+    {
+        nonLatentBlockMode = false;
+        input_position = 0;
+        output_position = 0;
+        memset(output_buffer, 0, sizeof(output_buffer));
+        memset(input_buffer, 0, sizeof(input_buffer));
+        memset(sidechain_buffer, 0, sizeof(sidechain_buffer));
+
+        setLatencySamples(BLOCK_SIZE);
+        updateHostDisplay(ChangeDetails().withLatencyChanged(true));
+    }
+
     auto mainInput = getBusBuffer(buffer, true, 0);
 
     int inChanL = 0;

src/surge-fx/SurgeFXProcessor.h

@@ -38,6 +38,7 @@ class SurgefxAudioProcessor : public juce::AudioProcessor,
     int output_position{-1};
 
     bool nonLatentBlockMode{true};
+
     //==============================================================================
     void prepareToPlay(double sampleRate, int samplesPerBlock) override;
     void releaseResources() override;