databases/cego: update 2.47.22 -> 2.47.24

• Replaced Chain("") with Chain() for several. This was motivated by an observed bug for check constraint xml import, where a comparision between Chain() and Chain("") returned false
• Fix in CegoFunction::evalFieldValue for case REPLACE. If replace string is null, then empty string is replaced instead of "null" string.

Author: Björn Lemke <lemke@lemke-it.com>