Invalid country names produce PHP warning for missing include file

A user submitted a node with the province value "NY" and left the country field blank. The country field was set as required, so a drupal error was shown instructing him to enter a country. But a php warning was also shown, because there's no such file location/supported/location.ny.inc.

I think location_load_country() should call location_supported_countries() to check for valid input.