Description:
------------
After processing an array containing pdo options with array_walk_recursive, the PDO constructor fails with
exception:

PDO::__construct(): SQLSTATE[HY000]: General error: attribute value must be an integer

According to vardump, the option array is perfectly fine. The assumption, that some internal structure get corrupted is triggered by the fact that by doing an is_integer() on the array values, the array becomes usable again.

The problem has been reproduced using 
PHP 7.1.1 (cli) ( NTS )
PHP 7.2.12 (cli) (built: Nov  6 2018 15:07:37) ( NTS )

It does not occur with
PHP 7.0.30-0+deb9u1 (cli) (built: Jun 14 2018 13:50:25) ( NTS )

Test script:
---------------
Find testscript at github:

https://gist.github.com/a-sassermann/840bd057f579169dc44bc4eee85b158a

It contains 3 tests:

1. check using PDO with unmodified option array
2. do an array_walk_recursive on option array before using with PDO
3. after array_walk_recursive do an is_integer() on array values

Expected result:
----------------
All tests should succeed without error.

Actual result:
--------------
Test 2 fails with exception 
PDO::__construct(): SQLSTATE[HY000]: General error: attribute value must be an integer