clapper-gtk: Fix metadata ignore for different languages

Since missing plugin string is translated, word describing its type
(e.g. Decoder) might come before plugin name itself, so we need to
check whole text to find substring instead of checking only prefix.

Fixes #477

src/lib/clapper-gtk/clapper-gtk-video.c

@@ -1065,7 +1065,7 @@ _player_missing_plugin_cb (ClapperPlayer *player, const gchar *name,
 {
   /* Some media files have custom/proprietary metadata,
    * it should be safe to simply ignore these */
-  if (g_str_has_prefix (name, "meta/"))
+  if (strstr (name, "meta/") != NULL)
     return;
 
   /* XXX: Playbin2 seems to not emit state change here,