demux_playlist: handle stream_read_line() errors

As of this commit, stream_read_line() can't actually error (except in
the case the passed in buffer is 0, which never happens here). This
commit is preparation for the following commit, which checks harder
whether the read data is actually text. Before this commit, an error
was treated as end-of-file, but the data read so far was considered
valid.

demux/demux_playlist.c

@@ -30,6 +30,7 @@ struct pl_parser {
     char buffer[8 * 1024];
     int utf16;
     struct playlist *pl;
+    bool error;
     bool probing;
 };
 
@@ -40,6 +41,8 @@ static char *pl_get_line0(struct pl_parser *p)
         int len = strlen(res);
         if (len > 0 && res[len - 1] == '\n')
             res[len - 1] = '\0';
+    } else {
+        p->error |= !p->s->eof;
     }
     return res;
 }
@@ -58,7 +61,7 @@ static void pl_add(struct pl_parser *p, bstr entry)
 
 static bool pl_eof(struct pl_parser *p)
 {
-    return p->s->eof;
+    return p->error || p->s->eof;
 }
 
 static int parse_m3u(struct pl_parser *p)
@@ -175,9 +178,10 @@ static int open_file(struct demuxer *demuxer, enum demux_check check)
     }
 
     p->probing = false;
+    p->error = false;
     p->s = demuxer->stream;
     p->utf16 = stream_skip_bom(p->s);
-    bool ok = fmt->parse(p) >= 0;
+    bool ok = fmt->parse(p) >= 0 && !p->error;
     if (ok)
         playlist_add_base_path(p->pl, mp_dirname(demuxer->filename));
     demuxer->playlist = talloc_steal(demuxer, p->pl);