session names must not be empty

The changes done in #58453 were not enough. Since the session name is used
as the cookie name it must not be the empty string.

Author: xabbuh

Tests/Session/Storage/Handler/AbstractRedisSessionHandlerTestCase.php

@@ -106,7 +106,7 @@ public function testUseSessionGcMaxLifetimeAsTimeToLive()
 
     public function testDestroySession()
     {
-        $this->storage->open('', '');
+        $this->storage->open('', 'test');
         $this->redisClient->set(self::PREFIX.'id', 'foo');
 
         $this->assertTrue((bool) $this->redisClient->exists(self::PREFIX.'id'));

Tests/Session/Storage/Handler/MemcachedSessionHandlerTest.php

@@ -119,7 +119,7 @@ public function testWriteSessionWithLargeTTL()
 
     public function testDestroySession()
     {
-        $this->storage->open('', '');
+        $this->storage->open('', 'sid');
         $this->memcached
             ->expects($this->once())
             ->method('delete')