Fix boolean to string convertation. Fix double normalization.

Hello!

I'm find and fix some bugs.

In details:
With the normalization of boolean values ​​and null, it is converted to the string "true" / "false" / "NULL", but this transformation should occur later - when formatting strings. Example
$context = ["false", false]; // formatted as {"0":"false","1":"false"} when need {"0":"false","1":false}

Normalization also occurs twice: first recursively on the entire array $record, followed by formatting strings in convertToString() method.

P.S.
Sorry for my bad English :-)