Fix AVAudioConverter callback to prevent buffer duplication

VoiceInk/AudioEngineRecorder.swift

@@ -169,11 +169,18 @@ class AudioEngineRecorder: ObservableObject {
         }
 
         var error: NSError?
+        var hasProvidedBuffer = false
 
         converter.convert(to: convertedBuffer, error: &error) { inNumPackets, outStatus in
+            if hasProvidedBuffer {
+                outStatus.pointee = .noDataNow
+                return nil
+            } else {
+                hasProvidedBuffer = true
                 outStatus.pointee = .haveData
                 return buffer
             }
+        }
 
         if let error = error {
             fileWriteLock.unlock()