Data cleaning sheets with only repeat question groups do not update the responses

[muloem]

When uploading a data cleaning sheet that only contains data from a repeat question group and no responses for the normal group(s) or a file with with only repeat question group sheet, the responses edited for data cleaning in the repeating group are never updated on the backend.

First sheet is empty

Data is only present for repeat question group

[stellanl]

Test plan:

1. Create a form with only one group which is repeatable.
2. Import both new and changed data to it.
3. Export it again and see that it was entered correctly.