Leveling ability inside the spellbook while it's owner is dead

[DracoL1ch]

Leveling ability inside the spellbook while it's owner is dead causes crash. No idea whats behind the game, yet it's simple as is. Add w/e checks there needed.
Repro: create spellbook, put any ability there
Jass: kill unit, increase level of ability inside the spellbook

 

[Daffa]

Well, that's quite interesting. Minor but quite dangerous since this is used in quite massive scale, making it major.