ffplay: dont wait 100ms if data is not yet ready

Also signal the wait if audio buffer is empty. This fixes jerky audio with
realtime sources.
Signed-off-by: Marton Balint <cus@passwd.hu>

ffplay.c

@@ -2586,7 +2586,9 @@ static int read_thread(void *arg)
                 eof = 1;
             if (ic->pb && ic->pb->error)
                 break;
-            SDL_Delay(100); /* wait for user event */
+            SDL_LockMutex(wait_mutex);
+            SDL_CondWaitTimeout(is->continue_read_thread, wait_mutex, 10);
+            SDL_UnlockMutex(wait_mutex);
             continue;
         }
         /* check if packet is in play range specified by user, then queue, otherwise discard */