[JENKINS-73554] fix jelly exception (jenkinsci#9519)

ensure that we don't get an IndexOutOfBoundsException when the
controller has no executors on cloud pages

core/src/main/resources/lib/hudson/executors.jelly

@@ -143,7 +143,7 @@ THE SOFTWARE.
                                       and !builtInHasExecutors)}"/>
   <!-- Remove the built-in from the list when it is included but has no executors to show -->
   <j:choose>
-    <j:when test="${!builtInHasExecutors and computers.get(0).node == app and computers.size() gt 1}">
+    <j:when test="${!builtInHasExecutors and computers.size() gt 1 and computers.get(0).node == app}">
       <j:set var="computers" value="${computers.subList(1, computers.size())}"/>
     </j:when>
   </j:choose>