flatpak_resolve_symlink: Properly make paths absolute

We need to use g_build_filename, g_build_path takes a separator
as the first arg, not a path!

common/flatpak-utils.c

@@ -2182,7 +2182,7 @@ flatpak_resolve_link (const char *path,
     return g_steal_pointer (&link);
 
   dirname = g_path_get_dirname (path);
-  return g_build_path (dirname, link, NULL);
+  return g_build_filename (dirname, link, NULL);
 }
 
 char *