player: fix initial osd progbar state

This made seeking show an empty progbar if --osd-level=0 was used.

player/main.c

@@ -288,6 +288,7 @@ static int mpv_main(int argc, char *argv[])
     *mpctx = (struct MPContext){
         .last_dvb_step = 1,
         .term_osd_contents = talloc_strdup(mpctx, ""),
+        .osd_progbar = { .type = -1 },
         .playlist = talloc_struct(mpctx, struct playlist, {0}),
     };