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.

[sekmiller]

Hi @plecor, Thanks for this PR. We have recently released version 6.5 of the Dataverse Software so please update your branch so that it will be ready for QA. Thanks again. (I am in the process of reviewing your submission, but it is likely that we won't be able to merge it until early in the coming year.)