If anonymous (not signed in user) requests page
"/:owner/:repo/pulls" he gets an error:
template: repo/issue/list:11:105: executing "repo/issue/list" at <.PullRequestCtx.Base...>: nil pointer evaluating *models.Repository.Link
This commit fixes that.
Signed-off-by: Dmitry Yu Okunev <dyokunev@ut.mephi.ru>