lib/utils: Check for invalid UTF-8 in filenames

In case a filename contains invalid UTF-8 characters, libostree will
pass it to g_variant_builder_add() in create_tree_variant_from_hashes()
anyway, which leads to a critical warning from glib and an invalid
commit. This commit makes ostree print a useful error and exit instead.

Closes: #1271
Approved by: cgwalters

src/libotutil/ot-unix-utils.c

@@ -47,6 +47,8 @@ ot_util_filename_validate (const char *name,
     return glnx_throw (error, "Invalid path uplink filename '..'");
   if (strchr (name, '/') != NULL)
     return glnx_throw (error, "Invalid / in filename %s", name);
+  if (!g_utf8_validate (name, -1, NULL))
+    return glnx_throw (error, "Invalid UTF-8 in filename %s", name);
   return TRUE;
 }