Fix interdiction not to wipe out target ship updates

Fix interdiction not to wipe out target ship updates

Ships can expend shells to defend against missiles, in
shp_missile_defense().  Any shell use by the target ship got wiped out
when shp_missile_interdiction() wrote back the target ship, triggering
a seqno mismatch oops.

Ships get updated when they launch planes to intercept interdicting
planes, in mission_pln_equip().  Any petrol use by the target ship got
wiped out when shp_mission_interdiction() wrote back the target ship,
triggering a seqno mismatch oops.

Fix by re-reading the target ship in shp_damage_one().  This also
affects shp_fort_interdiction(), where it is not necessary.  A bit
inefficient, but let's keep this fix simple.