Description:
------------
using Z_STRVAL_P before make sure it is IS_STRING:

see http://lxr.php.net/opengrok/xref/PHP_5_4/ext/mbstring/mbstring.c#3186

if (ZEND_NUM_ARGS() >= 2 && Z_STRVAL_P(encoding_list)) {
  		switch (Z_TYPE_P(encoding_list)) {
  		case IS_ARRAY:
  			if (FAILURE == 
php_mb_parse_encoding_array(encoding_list, &list, &size, 0 TSRMLS_CC)) {
  				if (list) {
  					efree(list);
  					list = NULL;
  					size = 0;
  				}
  			}
  			break;
  		default:
  			convert_to_string(encoding_list);
  			if (FAILURE == 
php_mb_parse_encoding_list(Z_STRVAL_P(encoding_list), Z_STRLEN_P(encoding_list), 
&list, &size, 0 TSRMLS_CC)) {
  				if (list) {
  					efree(list);
  					list = NULL;
  					size = 0;
  				}
  			}
  			break;
  		}
  		if (size <= 0) {
  			php_error_docref(NULL TSRMLS_CC, E_WARNING, "Illegal 
argument");
  		}
  	}

Test script:
---------------
none

Expected result:
----------------
none

Actual result:
--------------
none