add failsafe for no json in playht response

vocode/streaming/synthesizer/play_ht_synthesizer.py

@@ -82,27 +82,21 @@ async def create_speech_uncached(
                 timeout=ClientTimeout(total=15),
             )
             if not response.ok:
+                response_json = await response.json()
+                if response_json and "error_message" in response_json:
+                    message = response_json["error_message"]
+                else:
+                    message = f"Request to Play.HT failed with status code {str(response.status)}"
+
                 raise PlayHTV1APIError(
                     f"Play.ht API error status code {response.status}",
-                    (await response.json()).get(
-                        "error_message",
-                        f"Request to Play.HT failed with status code {str(response.status)}",
-                    ),
+                    message,
                 )
             if response.status == 429 and attempt < max_backoff_retries - 1:
                 await asyncio.sleep(backoff_retry_delay)
                 backoff_retry_delay *= 2  # Exponentially increase delay
                 continue
 
-            if not response.ok:
-                raise PlayHTV1APIError(
-                    f"Play.ht API error status code {response.status}",
-                    (await response.json()).get(
-                        "error_message",
-                        f"Request to Play.HT failed with status code {str(response.status)}",
-                    ),
-                )
-
             if self.experimental_streaming:
                 return SynthesisResult(
                     self.experimental_mp3_streaming_output_generator(