Previously we were listening to change in the appdata folder but an
appdata scan didn't setup the file system, so the view was unavailable.
**Test plan:**
1. rm -rf data/appdata_...../preview data/<user>/Media
2. occ files:scan-app-data
3. occ files:scan <user>
No errors and the files and metadata are correctly removed from the
database too.
Signed-off-by: Carl Schwan <carl@carlschwan.eu>
