only parse moves when position command line has at least three segments
only parse moves when position command line has at least three segments

Previously, we assumed that we would only get a startpos command containing
moves played, like `position startpos e2e3`. This seems to be good enough for
some UCI drivers (including XBoard), but others (at least Cute Chess) will also
issue a `position startpos` with no moves at the beginning of the game (even if
Cicada is playing black).

Resolves #3.

mkyl/cicada