fix(audio): initialize WriteFile before writing audio frames

- Add initialization check in WriteFile to ensure file is properly set up before writing
- Call initFile with filename when first writing audio frames
- Prevent potential errors from writing to an uninitialized file

shards/modules/audio/audio.cpp

@@ -1199,6 +1199,11 @@ struct WriteFile {
     if (input.payload.audioValue.channels != _channels) {
       throw ActivationError("Input has an invalid number of audio channels");
     }
+    if (!_initialized) {
+      const auto fname = SHSTRVIEW(_filename.get());
+      initFile(fname);
+      _initialized = true;
+    }
     ma_encoder_write_pcm_frames(&_encoder, input.payload.audioValue.samples, input.payload.audioValue.nsamples, NULL);
     return input;
   }