mplayer: don't call libquvi for local files

This is obviously not needed, and just creates potential for bad
breakages (e.g. what happens if libquvi tries to open a normal filename
as http URL?).

Note that for simplicity, we still pass file:// URIs to quvi, and we
don't exclude other protocol prefixes either. In general, we don't know
what protocols quvi might support, so we don't try to second-guess it.
(Even though in practice, it's probably only "http" and "https".)

mpvcore/mplayer.c

@@ -4251,6 +4251,8 @@ static void add_subtitle_fonts_from_sources(struct MPContext *mpctx)
 static struct mp_resolve_result *resolve_url(const char *filename,
                                              struct MPOpts *opts)
 {
+    if (!mp_is_url(bstr0(filename)))
+        return NULL;
 #if defined(CONFIG_LIBQUVI) || defined(CONFIG_LIBQUVI9)
     return mp_resolve_quvi(filename, opts);
 #else