Data Table Reimport - No popup to specify source file

Selecting Reimport on a DataTable created in editor no longer triggers selection popup.

"The change in behavior seems to be related to changes to UReimportDataTableFactory::CanReimport() which now returns (false) when there is no previously associated import file. This used to be handled by FReimportManager::ValidateAllSourceFileAndReimport() which allows CanReimport to either return an empty list of filenames or blank filenames."

Verified in MAIN at CL 4888291

1. Create a new BP Struct
2. Create a new DataTable based on Struct
3. Right-Click on DT and select "Reimport" (also tested with "Reimport with new file" in 4.22)

4.20 Result: Windows explorer appears allowing you to specify a source CSV

4.21+ Result: No window popup

Workaround - Export data table as CSV and import this file to Content Browser.