Currently, in both g_key_file_get_int64 and g_key_file_get_uint64, when g_ascii_strto(u)ll returns an error for parsing the value of a given key, rather than freeing the result of g_key_file_get_value, each function just returns. 

As it stands:

if (*s == '\0' || *end != '\0')
  {
    g_set_error (error, G_KEY_FILE_ERROR, G_KEY_FILE_ERROR_INVALID_VALUE, ...
    return 0;
  }

Should just be, in both cases:

if (*s == '\0' || *end != '\0')
  {
    g_set_error (error, G_KEY_FILE_ERROR, G_KEY_FILE_ERROR_INVALID_VALUE, ...
    g_free (s);
    return 0;
  }