Nextcloud's WebDAV server has no real per-file creation-time tracking
for most setups, so its creationdate property routinely comes back as
a placeholder Unix-epoch date ("Thu, 01 Jan 1970 00:00:00 GMT")
instead of being omitted. _parseDavDate parsed that "successfully"
into a real (if bogus) DateTime, so every item's dateCreated stuck at
the epoch instead of falling back to lastModified as it would for a
genuinely missing/unparseable value.
Add _parseDavCreationDate, which treats that placeholder the same as
an absent value, and use it at all four PROPFIND/SEARCH call sites
that read creationdate (folder listing, search, favorites, recent).