Ensure issue.Poster is loaded in mailIssueCommentToParticipants (#5891)
Ensure issue.Poster is loaded in mailIssueCommentToParticipants (#5891)

Previous code could potentially dereference nil - this PR ensures
that the poster is loaded before dereferencing it.

Signed-off-by: Andrew Thornton <6a547fdd28db89120bdd70d4af1f9ba672ccd43a@cantab.net>
typeless/gitea,lafriks/gitea,sapk-fork/gitea,sapk-fork/gitea,kubatyszko/gitea,cez81/gitea,vdbt/gitea,kubatyszko/gitea,go-gitea/gitea,cez81/gitea,typeless/gitea,vCaesar/gitea,cez81/gitea,vCaesar/gitea,typeless/gitea,lafriks/gitea,lafriks/gitea,go-gitea/gitea,sapk-fork/gitea,sapk-fork/gitea,typeless/gitea,go-gitea/gitea,vdbt/gitea,kubatyszko/gitea