SessionExtension: don't set readAndClose if null (#213)

Session class throws exception if session is started and option read_and_close is set.
SessionExtension breaks compatibility with other session implementations (in case they already started the session) by always setting that option (to default value).

src/Bridges/HttpDI/SessionExtension.php

@@ -91,6 +91,10 @@ public function loadConfiguration()
 			$options['autoStart'] = false;
 		}
 
+		if ($config->readAndClose === null) {
+			unset($options['readAndClose']);
+		}
+
 		if (!empty($options)) {
 			$session->addSetup('setOptions', [$options]);
 		}

src/Http/Session.php

@@ -405,7 +405,7 @@ public function setOptions(array $options)
 			$normalized[$normKey] = $value;
 		}
 
-		if (array_key_exists('read_and_close', $normalized)) {
+		if (isset($normalized['read_and_close'])) {
 			if (session_status() === PHP_SESSION_ACTIVE) {
 				throw new Nette\InvalidStateException('Cannot configure "read_and_close" for already started session.');
 			}