terraria crash: set single step mode, trigger an update, destroy a gate that is part of the current step

[slippycheeze]

I just triggered a crash, while debugging my wiring, by doing the following:

1. Set single step mode, no auto-step.
2. Build a five step "Compact Resetable Counter" from A reference guide to simple logic devices
3. Wire the final output to the reset line, so it self-resets at the end of the sequence.
4. Get to the state where the fourth output is active, so the next input will trigger the fifth output and self-reset the counter.
5. trigger the input line, which starts the mechscope single-step process.
6. step forward, so the logic activates all five of the gates at the bottom during reset
7. mine the left-most gate at the bottom, which is one of the "active" gates in the current single-step process
8. Terraria hangs in some sort of busy-wait state or something, presumably because one of the components of the current MechScope managed debugging process no longer exists.

I assume that can be simplified in obvious ways, but I figure it is better to report exactly what has been done than to try and guess if some random step may be important.