txd-gen: Fix bug creating temporary eids
txd-gen: Fix bug creating temporary eids

The first bug I feel I really discovered through generative testing.
Tempids should be negative, not 0. Therefore shift that range by one. I
wonder why datamic.api/tempid doesn't throw an exception, though. It
seems like (< n 0) could be a precondition.

rmoehn/theatralia,u-o/theatralia