[client] audio: harden playback at small period sizes

Bound playback writes and synchronization slews to the physical ring
storage, preventing overwritten samples from being treated as valid PCM.
Trigger clock resynchronization when output must be dropped.

Wait for enough startup audio to cover backend demand and a complete
source packet. Generate silence if playback begins early instead of
rewinding the reader into stale ring storage.

Honor PipeWire playback frame requests and fully initialize empty chunks.
This keeps playback reliable when using small device period sizes.

client/audiodevs/PipeWire/pipewire.c

@@ -140,19 +140,31 @@ static void pipewire_onPlaybackProcess(void * userdata)
   struct spa_buffer * sbuf = pbuf->buffer;
   uint8_t * dst;
 
-  if (!(dst = sbuf->datas[0].data))
+  if (sbuf->n_datas == 0 || !sbuf->datas[0].chunk ||
+      !(dst = sbuf->datas[0].data))
   {
+#if PW_CHECK_VERSION(1, 4, 0)
     pw_stream_return_buffer(pw.playback.stream, pbuf);
+#else
+    pw_stream_queue_buffer(pw.playback.stream, pbuf);
+#endif
     return;
   }
 
   int frames = sbuf->datas[0].maxsize / pw.playback.stride;
   if (pw.playback.rateMatch && pw.playback.rateMatch->size > 0)
     frames = min(frames, pw.playback.rateMatch->size);
+#if PW_CHECK_VERSION(0, 3, 50)
+  else if (pbuf->requested > 0)
+    frames = min(frames, pbuf->requested);
+#endif
 
   frames = pw.playback.pullFn(dst, frames);
   if (!frames)
   {
+    pbuf->size = 0;
+    sbuf->datas[0].chunk->offset = 0;
+    sbuf->datas[0].chunk->stride = pw.playback.stride;
     sbuf->datas[0].chunk->size = 0;
     pw_stream_queue_buffer(pw.playback.stream, pbuf);
     pipewire_updatePlaybackLatency();