Returns the value associated with
group_name as an integer.
key cannot be found then 0 is returned and throws is set to
g_key_file_error_key_not_found. Likewise, if the value associated with
key cannot be interpreted as an integer, or is out
of range for a int, then 0 is returned and throws is set to
a group name
the value associated with the key as an integer, or 0 if the key was not found or could not be parsed.