fix(security): PermissionHandler — fail CLOSED on custom-scope dispatch error

`dispatchCustomScopeEvaluation()` caught listener exceptions, logged
them, and returned `null` — letting the caller fall through to the
standard rule chain. For canonical verbs that's safe (chain decides),
but custom verbs (ZGW `besluit_nemen` etc.) explicitly delegate the
verdict to the listener; the chain has no opinion and "deny by
default" was the *intent*. The risk: when a listener has previously
voted ALLOW for a verb but the dispatcher itself throws, the cleared
verdict + chain-fallback can silently open access.

Treat the dispatcher exception as a deny vote (`return false`). A
genuinely down listener is a security event — let it surface as an
explicit denial rather than a no-op. Listener `deny()` votes that
land before the throw still propagate via the existing
`hasVerdict()` path.

Refs: #1419 review (concern 6) — discussion_r3187494479

Author: rubenvdlinde

lib/Service/Object/PermissionHandler.php

@@ -506,16 +506,26 @@ private function dispatchCustomScopeEvaluation(
         try {
             $this->eventDispatcher->dispatchTyped($event);
         } catch (Exception $e) {
+            // SECURITY: fail CLOSED. A listener exception means the app
+            // that owns the verdict for this verb is unavailable — for
+            // verbs the standard rule chain has no opinion on (the
+            // common case for custom verbs like ZGW `besluit_nemen`),
+            // falling through to "deny by default" is acceptable, but
+            // for verbs where a listener has previously voted ALLOW,
+            // returning null lets the standard chain re-decide and
+            // potentially open access. Treat the dispatcher exception
+            // itself as a deny vote so a crashed listener cannot
+            // upgrade-to-allow.
             $this->logger->warning(
-                message: '[PermissionHandler] CustomScopeEvaluatingEvent dispatch failed',
+                message: '[PermissionHandler] CustomScopeEvaluatingEvent dispatch failed — denying',
                 context: [
                     'file'   => __FILE__,
                     'line'   => __LINE__,
                     'action' => $action,
                     'error'  => $e->getMessage(),
                 ]
             );
-            return null;
+            return false;
         }
 
         if ($event->hasVerdict() === false) {