ProjectCommands.promptToImportImages always returns an empty list

[petebankhead]

Bug report

Describe the bug
ProjectCommands.promptToImportImages claims to return a list of imported images, but it appears that it does not.

To Reproduce
Steps to reproduce the behavior:

1. Run in an IDE using debug mode, with a breakpoint around

   qupath/qupath-gui-fx/src/main/java/qupath/lib/gui/QuPathGUI.java

   Line 3170 in f2a1f9c

   List<ProjectImageEntry<BufferedImage>> entries = ProjectCommands.promptToImportImages(this, pathNew);

2. Open a project
3. Drag a new image onto the project and agree to import it
4. Check the list contains the image (spoiler: it doesn't)

Expected behavior
A list is returned, as the docs suggest it should.

Or, if not possible (because the import is delayed), the method signature should be updated or there should be an async version explicitly provided.

Desktop (please complete the following information):

• OS: All, presumably
• QuPath Version: v0.4.3 (and likely before)

Additional context
Reported by @Rdornier at at https://forum.image.sc/t/prompttoimportimages-returns-empty-list-of-images/78112