User full-name search not working for mononymous names

**Describe the Bug**
The full name search for user names must be working in the same way for users with mononymous name(no first name) and users with first name and last name.

**Expected Behaviour**
The full name search for user names must be working in the same way for users with mononymous name(no first name) and users with first name and last name.

**Actual Behaviour**
User full-name search not working for mononymous names but working perfectly for other users who have both the names.

** Steps To Reproduce**
Steps to reproduce the behaviour:
1. Go to any data-table in SIMS which is server side paginated (e.g. pending exceptions in ministry portal)
2. Search by typing the name of a user who has mononymous name and also present in the data table.(e.g. jack)
3. The search result must not return any data pertaining to the searched user.

Start by reproducing the search in the server-side paginated pending-exceptions data-table in the ministry portal, then trace the search entry point to see how mononymous user names are handled. Done means searching for a name such as “jack” returns the matching user consistently with users who have first and last names.

Written by the indexing model from the issue text.