Make SVG size argument optional (#12814)

Now defaults to 16 on both frontend and backend.

Co-authored-by: techknowlogick <techknowlogick@gitea.io>

templates/admin/repo/list.tmpl

@@ -45,7 +45,7 @@
 							<td>
 								<a href="{{AppSubUrl}}/{{.Owner.Name}}">{{.Owner.Name}}</a>
 								{{if .Owner.Visibility.IsPrivate}}
-									<span class="text gold">{{svg "octicon-lock" 16}}</span>
+									<span class="text gold">{{svg "octicon-lock"}}</span>
 								{{end}}
 							</td>
 							<td><a href="{{AppSubUrl}}/{{.Owner.Name}}/{{.Name}}">{{.Name}}</a></td>