[HttpFoundation] Remove warnings when session id isn't given

src/Symfony/Component/HttpFoundation/SessionStorage/FilesystemSessionStorage.php

@@ -44,7 +44,7 @@ class FilesystemSessionStorage extends NativeSessionStorage
             $this->options['httponly']
         );
 
-        if (!ini_get('session.use_cookies') && $this->options['id'] && $this->options['id'] != session_id()) {
+        if (!ini_get('session.use_cookies') && isset($this->options['id']) && $this->options['id'] && $this->options['id'] != session_id()) {
             session_id($this->options['id']);
         }
 

src/Symfony/Component/HttpFoundation/SessionStorage/NativeSessionStorage.php

@@ -74,7 +74,7 @@ class NativeSessionStorage implements SessionStorageInterface
         // disable native cache limiter as this is managed by HeaderBag directly
         session_cache_limiter(false);
 
-        if (!ini_get('session.use_cookies') && $this->options['id'] && $this->options['id'] != session_id()) {
+        if (!ini_get('session.use_cookies') && isset($this->options['id']) && $this->options['id'] && $this->options['id'] != session_id()) {
             session_id($this->options['id']);
         }