ChessGame: fix type issue in getColourID
ChessGame: fix type issue in getColourID

The `getColourID` method could return `null` if the input `$colour`
was not one of the two expected values. To avoid this possibility,
and ensure that we always return an integer, use the `match` function
instead.

hemberger/smr,smrealms/smr,hemberger/smr,hemberger/smr,smrealms/smr,hemberger/smr,smrealms/smr