Move PHP session into captcha code to prevent unnecessary cookies.

post.php

@@ -169,9 +169,12 @@ elseif (isset($_GET['Newsgroups'])) {
 	error("NNTPChan: NNTPChan support is disabled");
 }
 
-session_start();
-if (!isset($_POST['captcha_cookie']) && isset($_SESSION['captcha_cookie'])) {
+// Create session cookie if not already done and captchas are enabled
+if ($config['captcha']['enabled'] || $config['report_captcha']) {
+	session_start();
+	if (!isset($_POST['captcha_cookie']) && isset($_SESSION['captcha_cookie'])) {
 		$_POST['captcha_cookie'] = $_SESSION['captcha_cookie'];
+	}
 }
 
 if (isset($_POST['delete'])) {