templates: hide detailed cache view with zero images

Hide the cache inspector when no cache elements are found in
neither of the selected clients.
Fix js exception caused by an array access in an empty image list.

ogcp/templates/actions/cache.html

@@ -49,11 +49,6 @@
         {{ _('Delete') }}
     </button>
 </form>
-{% else %}
-<div class="card text-center">
-    <b>{{ _('Cache is currently empty in the selected client(s)') }}</b>
-</div>
-{% endif %}
 
 <br>
 
@@ -195,4 +190,10 @@
     });
 </script>
 
+{% else %}
+<div class="card text-center">
+    <b>{{ _('Cache is currently empty in the selected client(s)') }}</b>
+</div>
+{% endif %}
+
 {% endblock %}