allow WIP marker to contains < or > (#4709)

Author: JulienTant

templates/repo/issue/new_form.tmpl

@@ -15,7 +15,7 @@
 					<div class="field">
 						<input name="title" id="issue_title" placeholder="{{.i18n.Tr "repo.milestones.title"}}" value="{{.title}}" tabindex="3" autofocus required>
 						{{if .PageIsComparePull}}
-							<span class="title_wip_desc">{{.i18n.Tr "repo.pulls.title_wip_desc" (index .PullRequestWorkInProgressPrefixes 0) | Safe}}</span>
+							<span class="title_wip_desc">{{.i18n.Tr "repo.pulls.title_wip_desc" (index .PullRequestWorkInProgressPrefixes 0| Escape) | Safe}}</span>
 						{{end}}
 					</div>
 					{{template "repo/issue/comment_tab" .}}