Wrap in exists check

This class isn't initialized if Polylang doesn't exist, but Polylang doesn't define pll_current_language if there aren't any languages, eg. you have a fresh installation and haven't configured it yet.

Author: k1sul1

classes/class-wplf-polylang.php

@@ -85,9 +85,13 @@ public function save_success_message( $message ) {
 
       return $message;
     }
-
+    
     public function ajax_object( $array ) {
-      $array['lang'] = pll_current_language();
+      if ( function_exists( 'pll_current_language' ) ) {
+        $array['lang'] = pll_current_language();
+      } else {
+        $array['lang'] = null;
+      }
       return $array;
     }