acap/coreaudio: fix outputting empty frames

a race condition

Prior to e511f898 (2024-11-14) and still in the stable branch, it
produces:
[Audio decompress] 2 empty channel(s) returned!

Author: MartinPulec

src/audio/capture/coreaudio.m

@@ -413,13 +413,13 @@ static void (^cb)(BOOL) = ^void(BOOL granted) {
         pthread_mutex_lock(&s->lock);
         ret = ring_buffer_read(s->buffer, s->frame.data, s->frame.max_size);
         if(!ret) {
+                s->data_ready = FALSE;
                 s->boss_waiting = TRUE;
                 while(!s->data_ready) {
                         pthread_cond_wait(&s->cv, &s->lock);
                 }
                 s->boss_waiting = FALSE;
                 ret = ring_buffer_read(s->buffer, s->frame.data, s->frame.max_size);
-                s->data_ready = FALSE;
         }
         pthread_mutex_unlock(&s->lock);