Fixes SQLite migration with non-null column.

This reverts commit 6a1a4880.

Testplan:
- [ ] Without: Accessing `public.php?service=files&t=` throws an exception
- [ ] With: No exception thrown and 404 page displayed.

Fixes https://github.com/owncloud/core/issues/14231

Reasoning:
- a WebDAV server is not required to implement locking support
- WebDAV Locking is know to break the sync algorithm
- the current lock implementation is known to be broken (locks are not moved if a file is moved, locks on shared files don't work)

'files' is neither used in the controller or the template

My IDE was crying...

Introduced with https://github.com/owncloud/core/commit/1df8a5a774ae5d665849daf74540d967826d5e11 in February 2013…

Breaking change for 8.1 wiki (Security > Administrators):

The log format for failed logins has changed and uses now the remote address and is considering reverse proxies for such scenarios when configured correctly.

A missing "n" was added in line 63.

The encryption webdav tests are too broad and do not qualify as unit
test. Also, since the sabre upgrade they are not fixable.
The matching functionality is already tested in other classes on a
smaller scale.

- VObject fixes for Sabre\VObject 3.3
- Remove VObject property workarounds
- Added prefetching for tags in sabre tags plugin
- Moved oc_properties logic to separate PropertyStorage backend (WIP)
- Fixed Sabre connector namespaces
- Improved files plugin to handle props on-demand
- Moved allowed props from server class to files plugin
- Fixed tags caching for files that are known to have no tags
  (less queries)
- Added/fixed unit tests for Sabre FilesPlugin, TagsPlugin
- Replace OC\Connector\Sabre\Request with direct call to
  httpRequest->setUrl()
- Fix exception detection in DAV client when using Sabre\DAV\Client
- Added setETag() on Node instead of using the static FileSystem
- Also preload tags/props when depth is infinity

This checks if the offset exists before accessing it and also adds unit tests to this function which would have catched this before 

Fixes https://github.com/owncloud/core/issues/14277