Deadlock detection for supply fail-case

[rtwong]

If the build order goal has a queued nexus/pylon, and the probe has the action called to go put down this supply structure, but then is killed onroute, the pylon/nexus is removed from the build order goal like desired, however a flag that says whether or not a supplybuilding is building is not properly reset, making it so that the deadlock check returns the incorrect answer.

This bug is most easily noticed when the bot tries to expand for the first time at ~40 supply, if the probe is intercepted no more pylons will be attempted to be built even when supply blocked.

[davechurchill]

Thanks, will look into it