Merge commit '2c3f29c4'

* commit '2c3f29c4':
  xcbgrab: Support empty filename string correctly

Conflicts:
	libavdevice/xcbgrab.c

See: 62eca2f8Merged-by: Michael Niedermayer <michaelni@gmx.at>

libavdevice/xcbgrab.c

@@ -613,11 +613,11 @@ static av_cold int xcbgrab_read_header(AVFormatContext *s)
         sscanf(s->filename, "+%d,%d", &c->x, &c->y);
     }
 
-    c->conn = xcb_connect(display_name, &screen_num);
+    c->conn = xcb_connect(display_name[0] ? display_name : NULL, &screen_num);
     av_freep(&display_name);
     if ((ret = xcb_connection_has_error(c->conn))) {
         av_log(s, AV_LOG_ERROR, "Cannot open display %s, error %d.\n",
-               (*s->filename) ? s->filename : "default", ret);
+               s->filename[0] ? s->filename : "default", ret);
         return AVERROR(EIO);
     }
     setup = xcb_get_setup(c->conn);