Fix typos and ensure odd-numbered channels have odd numbers

[jes]

The logic in availableOutboundChannelId ensured that when a channel needs an even number, an even number is generated, but it did not ensure that when a channel needs an odd number, an odd number is generated.

It worked anyway, so probably the only time it ever needs an odd-numbered id, the number 1 would do, but it seems right to fix the logic anyway.