Fixed incinerate on defense

[Toranks]

In rare cases, when the unit is already dead and the incinerate event try to do unstore_unit here, you get an error on the screen and various errors in the log:

20230428 15:43:48 error engine: failed to auto-store $unit at (39,26)
20230428 15:43:48 error engine: failed to auto-store $unit at (39,26)
20230428 15:43:48 error wml: [unstore_unit]: variable 'unit' doesn't contain unit data

20230428 15:43:48 error engine: failed to auto-store $unit at (39,26)
20230428 15:43:48 error engine: failed to auto-store $unit at (39,26)
20230428 15:43:48 error engine: failed to auto-store $unit at (39,26)
20230428 15:43:48 error engine: failed to auto-store $unit at (39,26)

To avoid this, simply use the same method as in the attacker_hits incinerate event, with the conditional

         [if]
             [have_unit]
                 find_in=unit
             [/have_unit]

[have_unit] will filter out units that are still alive after the attack. If the unit is died, the filter will do negative and it will stop.

[Dugy]

Thanks for fixing it.