fix template bug on mirror repository setting page (#8438)

modules/templates/helper.go

 		"CommentMustAsDiff": gitdiff.CommentMustAsDiff,
 		"MirrorAddress":     mirror_service.Address,
 		"MirrorFullAddress": mirror_service.AddressNoCredentials,
+		"MirrorUserName":    mirror_service.Username,
+		"MirrorPassword":    mirror_service.Password,
 	}}
 }
 

templates/repo/settings/options.tmpl

 							<i class="icon dropdown"></i>
 							<label for="">{{.i18n.Tr "repo.need_auth"}}</label>
 						</label>
-						<div class="content {{if .Err_Auth}}active{{else if .Mirror.Username}}active{{end}}">
+						<div class="content {{if .Err_Auth}}active{{else if (MirrorUserName .Mirror)}}active{{end}}">
 							<div class="inline field {{if .Err_Auth}}error{{end}}">
 								<label for="mirror_username">{{.i18n.Tr "username"}}</label>
-								<input id="mirror_username" name="mirror_username" value="{{.Mirror.Username}}" {{if not .mirror_username}}data-need-clear="true"{{end}}>
+								<input id="mirror_username" name="mirror_username" value="{{MirrorUserName .Mirror}}" {{if not .mirror_username}}data-need-clear="true"{{end}}>
 							</div>
 							<input class="fake" type="password">
 							<div class="inline field {{if .Err_Auth}}error{{end}}">
 								<label for="mirror_password">{{.i18n.Tr "password"}}</label>
-								<input id="mirror_password" name="mirror_password" type="password" value="{{.Mirror.Password}}" {{if not .mirror_password}}data-need-clear="true"{{end}}>
+								<input id="mirror_password" name="mirror_password" type="password" value="{{MirrorPassword .Mirror}}" {{if not .mirror_password}}data-need-clear="true"{{end}}>
 							</div>
 						</div>
 					</div>