Issue 50620 - Fix regressions from 50506 (slapi_enry_attr_get_ref)
Description: Some crashes were found in upstream testing. Needed
to revert slapi_entry_attr_get_ref() back to slapi_entry_attr_get_charptr()
relates: https://pagure.io/389-ds-base/issue/50620
Reviewed by: tbordaz(Thanks!)