audio: fix race condition in EOF code

Don't return an EOF code if there's still buffered data.

Also, don't call demux_stream_eof() in the playloop. There's probably
nothing wrong with it, but it's cleaner not to use it.

Also give AD_EOF its own value, so that a decoding error doesn't drain
audio by causing an EOF condition.

audio/decode/dec_audio.c

@@ -274,13 +274,13 @@ static int filter_n_bytes(struct dec_audio *da, struct mp_audio_buffer *outbuf,
     filter_data.rate = da->afilter->input.rate; // due to playback speed change
     len = MPMIN(filter_data.samples, len);
     filter_data.samples = len;
-    bool eof = filter_data.samples == 0 && error < 0;
+    bool eof = error == AD_EOF && filter_data.samples == 0;
 
     if (af_filter(da->afilter, &filter_data, eof ? AF_FILTER_FLAG_EOF : 0) < 0)
         return AD_ERR;
 
     mp_audio_buffer_append(outbuf, &filter_data);
-    if (eof && filter_data.samples > 0)
+    if (error == AD_EOF && filter_data.samples > 0)
         error = 0; // don't end playback yet
 
     // remove processed data from decoder buffer:

audio/decode/dec_audio.h

@@ -51,9 +51,9 @@ struct dec_audio {
 enum {
     AD_OK = 0,
     AD_ERR = -1,
-    AD_EOF = -1, // same as AD_ERR for now
     AD_NEW_FMT = -2,
     AD_ASYNC_PLAY_DONE = -3,
+    AD_EOF = -4,
 };
 
 struct mp_decoder_list *audio_decoder_list(void);

player/audio.c

@@ -427,7 +427,7 @@ int fill_audio_out_buffers(struct MPContext *mpctx, double endpts)
             return -1;
         } else if (res == AD_ASYNC_PLAY_DONE)
             return 0;
-        else if (demux_stream_eof(d_audio->header))
+        else if (res == AD_EOF)
             audio_eof = true;
     }