Fix some wrong return values in mob skill code

[Kenpachi2k13]

Pull Request Prelude

• I have followed proper Hercules code styling.
• I have read and understood the contribution guidelines before making this PR.
• I am aware that this PR may be closed if the above-mentioned criteria are not fulfilled.

Changes Proposed

• Fix return value evaluation of mob_skill_use() in mob_ai_sub_hard().
• Fix nullpo-check return values in mob_skill_use().
• Fix nullpo-check return values and initial value of variable ret in mobskill_event().
• Rename mob->skill_use() to mob->use_skill() due to changed return values.
• Rename mob->skill_event() to mob->use_skill_event() due to changed return values.

Issues addressed: None.

[skyleo]

What confuses me a bit about this PR is that I see no commit that is purely dedicated to changing the return value logic.
But there's commits that rename functions due to their return value logic having changed. Can you post a reference to the previous commits that I need to know for this?

[skyleo]

mob_use_skill has a typo in it's documentation btw.

[Kenpachi2k13]

What confuses me a bit about this PR is that I see no commit that is purely dedicated to changing the return value logic.
But there's commits that rename functions due to their return value logic having changed. Can you post a reference to the previous commits that I need to know for this?

Aye-aye, sir!
452b603

mob_use_skill has a typo in it's documentation btw.

Captain eagle eye. 😆
I'll fix it....

[skyleo]

@Kenpachi2k13 I think you have to set res = 1 in mobskill_event as well due to how the return values changed.
I see you did that here already. hehe

[Kenpachi2k13]

@Kenpachi2k13 I think you have to set res = 1 in mobskill_event as well due to how the return values changed.

I did. 😮
521ca00

But thanks to your comment I just realised that I forgot to separate the declaractions of target_id and res. 👍