Prevent NPE in MyData when all dataverses are harvested dataverses

[plecor]

What this PR does / why we need it:
As discussed in #11083, MyData was checking for empty results and then filtering against harvested dataverses, producing a NullPointerException later on when all the results are harvested dataverses.

This moves the empty results check after filtering against harvested dataverses, resulting in a 'Sorry, no results were found." API response instead of the previous server error.

Which issue(s) this PR closes:
This improves #11083 but does not close it (non-harvested datasets in harvested dataverses are still filtered).

Special notes for your reviewer:
See the issue for steps to reproduce.

Suggestions on how to test this:

Does this PR introduce a user interface change? If mockups are available, please link/include them here:
No interface change

Is there a release notes update needed for this change?:
This could be mentioned (see snippet) but has no major impact.

Additional documentation:

I updated the IT test with some extra use cases. I'm not actually testing the harvested dataverse case as I am not sure if the expected result is truly the same as the current result.

Bug mentioned at https://dataverse-guide--11086.org.readthedocs.build/en/11086/api/native-api.html#mydata

[coveralls]

coverage: 22.571%. remained the same
when pulling 40a2080 on plecor:11083-mydata-npe-with-harvested-dataverses
into a4d0127 on IQSS:develop.

[pdurbin]

@plecor thanks for the PR! ❤️ We'll talk about it soon in a bug triage meeting. I went ahead and threw a small size (3) on it.

testDeleteFile is failing but please don't worry about that. It's unrelated and we plan to fix it in #11081.