Add missed return after ctx.ServerError (#31130) (#31133)

Backport #31130 by @lunny

Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>

routers/web/org/projects.go

@@ -571,6 +571,7 @@ func MoveIssues(ctx *context.Context) {
 	form := &movedIssuesForm{}
 	if err = json.NewDecoder(ctx.Req.Body).Decode(&form); err != nil {
 		ctx.ServerError("DecodeMovedIssuesForm", err)
+		return
 	}
 
 	issueIDs := make([]int64, 0, len(form.Issues))