committing check for empty object property during array-to-object castin...

This is a fix for bug #67300:

URL: https://bugs.php.net/bug.php?id=67300

The following files need to be pulled for the fix:

Zend/zend_operators.c
tests/lang/operators/bug67300.phpt
It's better to use the `%s` format specifier here and use `EXPECTF`