Fix error when we can not generate random string

Fixes #12056

Signed-off-by: Michal Čihař <michal@cihar.com>

ChangeLog

@@ -47,6 +47,7 @@ phpMyAdmin - ChangeLog
 - issue #11907 Avoid displaying UPDATE query twice
 - issue #11850 Fixed CSV import
 - issue        Fix SQL syntax highlighting in database search page
+- issue #12056 Fix error when we can not generate random string
 
 4.5.5.1 (not yet released)
 - issue #11971 CREATE UNIQUE INDEX index type is not recognized by parser.

libraries/session.inc.php

@@ -117,5 +117,13 @@ if (! isset($_SESSION[' PMA_token '])) {
         $_SESSION[' PMA_token '] = bin2hex(openssl_random_pseudo_bytes(16));
     }
 }
+/**
+ * Check if token is properly generated (both above functions can return false).
+ */
+if (empty($_SESSION[' PMA_token '])) {
+    PMA_fatalError(
+        'Failed to generate random CSRF token!'
+    );
+}
 
 require_once 'libraries/session.lib.php';