Fix memory leak of prepared queries

[stavikpetr]

When a query is prepared with ibase_prepare() and then it is freed with ibase_free_query(), the associated zend_resource object is never freed, because the function ibase_free_query() does not decrease its ref count and it stays forever at 1 (after all the variables holding reference in php are destroyed).

I was also considering to use a following fix:

uint32_t refcount = GC_REFCOUNT(Z_RES_P(query_arg));
zend_list_close(Z_RES_P(query_arg));
if (refcount > 0) {
	zend_list_delete(Z_RES_P(query_arg));
}

This solution would avoid memory access violations in cases when the refcount is already 0 (because the zend_resource would get freed in zend_list_close()), but I would argue that this situation should never occurr and it could happen only if the internal reference created during ibase_prepare() was freed by some other parts of the code. But that is not correct and instead, it should be always freed only here.

[MartinKoeditz]

@stavikpetr Thank you. I will check and merge your patch next week.