auhal: prevent assertion failure on TPCircularBufferClear (close #10109)

modules/audio_output/auhal.c

@@ -1379,20 +1379,22 @@ static void Flush(audio_output_t *p_aout, bool wait)
 {
     struct aout_sys_t *p_sys = p_aout->sys;
 
+    int32_t availableBytes;
+    vlc_mutex_lock(&p_sys->lock);
+    TPCircularBufferTail(&p_sys->circular_buffer, &availableBytes);
+
     if (wait) {
-        int32_t availableBytes;
-        vlc_mutex_lock(&p_sys->lock);
-        TPCircularBufferTail(&p_sys->circular_buffer, &availableBytes);
         while (availableBytes > 0) {
             vlc_cond_wait(&p_sys->cond, &p_sys->lock);
             TPCircularBufferTail(&p_sys->circular_buffer, &availableBytes);
         }
-        vlc_mutex_unlock(&p_sys->lock);
-
     } else {
-        /* flush circular buffer */
-        TPCircularBufferClear(&p_aout->sys->circular_buffer);
+        /* flush circular buffer if data is left */
+        if (availableBytes > 0)
+            TPCircularBufferClear(&p_aout->sys->circular_buffer);
     }
+
+    vlc_mutex_unlock(&p_sys->lock);
 }
 
 static int TimeGet(audio_output_t *p_aout, mtime_t *delay)