frame_processor: make sure clock is initialized

src/pipecat/processors/frame_processor.py

@@ -260,7 +260,7 @@ class FrameProcessor:
 
     async def __internal_push_frame(self, frame: Frame, direction: FrameDirection):
         try:
-            timestamp = self._clock.get_time()
+            timestamp = self._clock.get_time() if self._clock else 0
             if direction == FrameDirection.DOWNSTREAM and self._next:
                 logger.trace(f"Pushing {frame} from {self} to {self._next}")
                 if self._observer: