Fix PHP error when checking for impersonation without authentication.

Author: ADmad

src/Controller/Component/AuthenticationComponent.php

@@ -445,6 +445,10 @@ public function stopImpersonating()
      */
     public function isImpersonating(): bool
     {
+        if (!$this->getIdentity()) {
+            return false;
+        }
+
         $service = $this->getImpersonationAuthenticationService();
         $controller = $this->getController();
 

tests/TestCase/Controller/Component/AuthenticationComponentTest.php

@@ -731,13 +731,17 @@ public function testIsImpersonating()
         $this->request->getSession()->write('AuthImpersonate', $impersonator);
         $this->service->authenticate($this->request);
         $request = $this->request
-            ->withAttribute('authentication', $this->service);
+            ->withAttribute('authentication', $this->service)
+            ->withAttribute('identity', new Identity($impersonated));
         $controller = new Controller($request, $this->response);
         $registry = new ComponentRegistry($controller);
         $component = new AuthenticationComponent($registry);
 
         $result = $component->isImpersonating();
         $this->assertTrue($result);
+
+        $component->logout();
+        $this->assertFalse($component->isImpersonating());
     }
 
     /**