fix error of merge chunks

transcribe/strategy.py

@@ -309,11 +309,12 @@ class TranscriptStabilityAnalyzer:
         logger.debug(f"Current separator: {self._separator}")
 
     def merge_chunks(self, chunks: List[TranscriptChunk])->str:
+        if not chunks:
+            return [""]
         output =  list(r.join() for r in chunks if r)
         return output
 
 
-
     def analysis(self, current: TranscriptChunk, buffer_duration: float) -> Iterator[TranscriptResult]:
         current = TranscriptChunk(items=current, separator=self._separator)
         self._transcript_history.add(current)