Fix panic when view issue without login

routers/repo/issue.go

@@ -254,11 +254,13 @@ func ViewIssue(ctx *middleware.Context, params martini.Params) {
 		}
 	}
 
+	if ctx.IsSigned {
 		// Update issue-user.
 		if err = models.UpdateIssueUserPairByRead(ctx.User.Id, issue.Id); err != nil {
 			ctx.Handle(500, "issue.ViewIssue(UpdateIssueUserPairByRead): %v", err)
 			return
 		}
+	}
 
 	// Get poster and Assignee.
 	if err = issue.GetPoster(); err != nil {