Generate correct ARG_INFO of getter

[Jeckerson]

Current code:

protected transaction = null { get };

will generate incorrect ARG_INFO which will cause seg fault:

ZEND_BEGIN_ARG_WITH_RETURN_TYPE_INFO_EX(arginfo_phalcon_mvc_model_gettransaction, 0, 0, IS_NULL, 1)
ZEND_END_ARG_INFO()

It is impossible to have IS_NULL inside 4th argument of ZEND_BEGIN_ARG_WITH_RETURN_TYPE_INFO_EX it always must contain valid namespace class.

[Jeckerson]

Fixed in #2387