parser infinite loop with stray case statement

This causes an infinite loop with or without --keep-going.

void main() {
    case 1:
}

% vala iloop.vala
iloop.vala:2.5-2.8: error: expected `}'
iloop.vala:2.5-2.8: error: expected end of file
iloop.vala:2.5-1.13: error: The root namespace already contains a definition for `main'
iloop.vala:2.5-2.8: error: expected end of file
...