Update Tokenizer.php

`Trying to access array offset on value of type null` Exception fix in php >= 7.4

src/Fenom/Tokenizer.php

@@ -254,6 +254,9 @@ class Tokenizer
      */
     public function current()
     {
+        if (is_null($this->curr)) {
+            return null;
+        }
         return $this->curr[1];
     }