Handle empty sections in AnswerTree

[emmatekulova]

Description

Related issue: #1563

Motivation and Context

Solving issue.

How has this been tested?

Reproduced the bug with a catalog containing an empty section. Found the error message - after it is not there.

Screenshots (if appropriate)

Before:

After

[coveralls]

coverage: 94.901%. remained the same — emmatekulova:2.4.4/fix/empty-section-answer-tree into rdmorganiser:main

[MyPyDavid]

Hello @emmatekulova, thanks for joining the Sprint and creating this PR with the bug fix for RDMO.
We are looking if we want to add more tests to cover this case or if we need to add more conditionals to this fix but we can definitively take your commit in our next release!
Only thing is that we need to rebase this branch to the current 2.5.0/release branch (it has some merge conflicts that I need to solve) or we make a new branch 2.5.0/fix/empty-section-answer-tree (and PR) from the 2.5.0/release and cherry pick this commit onto it (which you or we could also do if you want to).
I forgot to check for this on Monday 😅

[jochenklar]

Hi @emmatekulova thanks for helping us! I created 2 tests which test the bug and which we can merge after your patch: #1585