avfilter/vf_fieldhint: use av_fopen_utf8()

libavfilter/vf_fieldhint.c

@@ -65,7 +65,7 @@ static av_cold int init(AVFilterContext *ctx)
         av_log(ctx, AV_LOG_ERROR, "Hint file must be set.\n");
         return AVERROR(EINVAL);
     }
-    s->hint = fopen(s->hint_file_str, "r");
+    s->hint = av_fopen_utf8(s->hint_file_str, "r");
     if (!s->hint) {
         ret = AVERROR(errno);
         av_log(ctx, AV_LOG_ERROR, "%s: %s\n", s->hint_file_str, av_err2str(ret));