Interface improvement for area fire

[Mobhack]

from the version 12 release notes:

A code quirk, some might call it a bug, that allowed players, particularly PBEM players, the ability to Z-Fire or X- Smoke into a hex with on map artillery then go to the bombardment menu and get a 0.1 delay for a full bombardment has been eliminated. It is no longer possible to do that and a side benefit for some players, but perhaps not to the players who loved to do "recon by Z-fire", is that it is no longer possible to Z-fire into a hex then repeat, repeat, repeat using the F key. Every Z fire now needs to be done individually because after a Z-fire the process is now reset to zero after each Z-Fire so that hex cannot be used to circumvent the artillery bombardment routine delay.

So no, the indirect fire hex for the unit is deliberately nullified per Z or X fire shot in order that it cannot be used for the above.