fix(groups): avoid panic on nil options and empty avatar in CreateGroup/UpdateGroup (!3135) · Merge requests · GitLab.org / API / client-go

Guard opt != nil in CreateGroup and UpdateGroup, so nil options no longer panic on opt.Avatar.
CreateGroup now skips the upload for an empty GroupAvatar{}, matching UpdateGroup. Before, withUpload(nil, ...) made io.Copy panic.
Tests cover nil options on create and update, plus an empty avatar on create.

Fixes #2331

fix(groups): avoid panic on nil options and empty avatar in CreateGroup/UpdateGroup