BUG: don't try to update null database

[pieper]

Retrieve database is not created when there are no
studies selected leading to a crash.

Now there is no attempt to update a null database.

Slicer/Slicer#5244

[xriobe]

We could exit earlier if d->dicomTableManager->currentStudiesSelection() is empty ?

[pieper]

We could exit earlier if d->dicomTableManager->currentStudiesSelection() is empty ?

That's what happens in effect. The for loop never gets entered so the operation completes instantly.

[xriobe]

We could exit earlier if d->dicomTableManager->currentStudiesSelection() is empty ?

That's what happens in effect. The for loop never gets entered so the operation completes instantly.

I was thinking even at the beginning of the method, before the creation of the progress dialog and the ctkDICOMRetrieve, but that's fine like this too.

[pieper]

Thanks for the review. Since this is a small change I'm not going to update Slicer's superbuild yet. This will get included in the next update.