Update IO_DFPlayer.h

Ensure device goes off-line when not responding.

IO_DFPlayer.h

@@ -231,11 +231,13 @@ protected:
         // Poll device every second that other commands aren't being sent,
         // to check if it's still connected and responding.
         sendPacket(0x42); 
+        if (!_awaitingResponse) {
           _timeoutTime = currentMicros + 5000000UL;  // Timeout if no response within 5 seconds
           _awaitingResponse = true;
         }
       }
     }
+  }
 
   // Write with value 1 starts playing a song.  The relative pin number is the file number.
   // Write with value 0 stops playing.