Description:
------------
When decoding a JSON encoded string which contains a special character like ? or ?, json_decode() returns a null.

Reproduce code:
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$foo = '[{"city":"gen?ve"}]';
$obj = json_decode($foo);
var_dump($obj);

Expected result:
----------------
array
  0 => 
    object(stdClass)[1]
      public 'city' => string 'gen?ve' (length=6)


Actual result:
--------------
null