Don't display select all issues checkbox when no issues are availab…

…le (go-gitea#25086)

Before:

![image](https://github.com/go-gitea/gitea/assets/1969460/8830c077-89d4-4897-a6e0-f5dba6830ff7)

After:

![image](https://github.com/go-gitea/gitea/assets/1969460/8fa06878-496b-4f65-87eb-04e1f94d4a3c)

templates/repo/issue/list.tmpl

@@ -83,7 +83,7 @@
 		</div>
 		<div id="issue-filters" class="issue-list-toolbar">
 			<div class="issue-list-toolbar-left">
-				{{if $.CanWriteIssuesOrPulls}}
+				{{if and ($.CanWriteIssuesOrPulls) (gt (len .Issues) 0)}}
 					<input type="checkbox" autocomplete="off" class="issue-checkbox-all gt-mr-4" title="{{.locale.Tr "repo.issues.action_check_all"}}">
 				{{end}}
 				{{template "repo/issue/openclose" .}}