core-desktop: file dialog defaults to wrong download location

[hellsworth]

I have the simple-scan snap in candidate (44.0, Rev 792) on a core desktop system. When I scan a document and click the download button, the default location it tries to open, as a suggested download location, gives a permissions error. This is because the default location opened is /run/user/1001/doc, which nobody will have access to.

You can still click OK and then go select another location like ~/Downloads and download the document just fine though.