When checking for public (web) access to the data directory the status is not enough
as you might have a webserver that forwards to e.g. a login page.
So instead check that the content of the file matches.
For this the `.ncdata` file (renamed from `.ocdata`¹) has minimal text content
to allow checking.
¹The file was renamed from the legacy `.ocdata`, there is a repair step to remove the old one.
Signed-off-by: Ferdinand Thiessen <opensource@fthiessen.de>
