Getting attacked while receiving training from NPC loses all progress

Game version: 420b8c35b0336e627cf3186d2b6ee9d38aeb8eab

Operating system: GNU/Linux

Tiles or curses: tiles

Mods active: Default

### Expected behavior
If you receive training from an NPC, but you get attacked and choose to abort the training, the NPC lets you continue the training (under normal circumstances).

### Actual behavior
If you abort the training for any reason (i.e. you get attacked), the training is lost forever, thus you wasted your money or your reward for completing a mission.

### Steps to reproduce the behavior
* Finish a mission an NPC gave you
* Choose training as a reward
* Get attacked while training

No source file, test, or entry point is named. Start by reproducing the NPC training flow with the Default mods on tiles, then trace what happens when an attack interrupts and training is aborted. Done means the paid or mission-earned training remains available so the NPC can resume it afterward.

Written by the indexing model from the issue text.