fixed playht3.0 cannot be played if credential is cached

lib/synth-audio.js

@@ -779,6 +779,9 @@ const synthPlayHT = async(client, logger, {
         synthesizeUrl = inference_address;
         const expiry =  Math.floor((expires_at_ms - Date.now()) / 1000 - 30);
         await client.set(key, inference_address, 'EX', expiry);
+      } else {
+        // Use cached URL
+        synthesizeUrl = url;
       }
     } catch (err) {
       logger.info({err}, 'synth PlayHT returned error for authentication version 3.0');