update ``.raw-content`` when edit issue/comment content (#16021)
update ``.raw-content`` when edit issue/comment content (#16021)

* update ``.raw-content`` when edit issue/comment content

fix #16000

Signed-off-by: a1012112796 <0a2492404be0c6c42b907cdcd1cb97449035f950@qq.com>

* handle empty content

Co-authored-by: techknowlogick <274271a2414b6bd0d2eb0401dd4ff6e85d7016a7@gitea.io>
go-gitea/gitea,go-gitea/gitea,vdbt/gitea,go-gitea/gitea,vdbt/gitea