Player does not get loot when entity promotes while killing stuff.

[Freagarach]

As noticed by @Angen in ​D2281 when a unit promotes while killing an enemy by a Status Effect the player does not receive loot.

The edge case in vanilla (A23b as well as current SVN) where this happens is when a unit fires a killing arrow and, while the arrow still flies, the unit promotes (by a tech). When the arrow hits and kills the target the attacking player does not receive loot due to Attacking.js L317 being undefined (the original attacking entity is gone).

(See also #4595 and ​D558. Perhaps ​D2330.)