Fix infinite propfinds reporting files as directories

[nickvergessen]

Backport of #55

Since it's quite criticla for a lot of apps that use our webdav endpoint.

[MorrisJobke]

For me this works already on stable11:

curl --request PROPFIND \
  --url 'http://192.168.99.100/server/remote.php/webdav/dsf?=' \
  --header 'authorization: Basic YWRtaW46YWRtaW4=' \
  --header 'content-type: application/xml' \
  --cookie 'cookie_test=test; occ1lehs6bp5=80d7t19mkh4j6agr73ktret4f2; oc_sessionPassphrase=BikTn10iZpdr6dgTbQynX9DAKLhed8wF8sNe98Zy6g9Q673b%252FOgV0Q5c%252Bc2dTIilDaqvkh%252BYCt%252BJkijVk1pOEjf5ymfOzH46Bxt778UGIZoN%252Fsi%252FSdjAugZddhG0oFeh; nc_sameSiteCookielax=true; nc_sameSiteCookiestrict=true; oc95fh0ebnef=kbu16s21li0l468k75jnpl7sq7; ocv78sh130w7=32oiug42nemh80t2r1hl087rn6; ockhugh6eb86=rr42qp520c62dh85r4ldrasnb7; ocgrs9o0f136=lj5gfidhcc178blbngqv75a897; PHPSESSID=u9nvkn374smr9ab0vgtdoo0io1' \
  --data '<?xml version="1.0"?>\n<d:propfind xmlns:d="DAV:">\n  <d:prop>\n    <d:resourcetype />\n  </d:prop>\n</d:propfind>'

The response is:

<?xml version="1.0"?>
<d:multistatus
	xmlns:d="DAV:"
	xmlns:s="http://sabredav.org/ns"
	xmlns:oc="http://owncloud.org/ns"
	xmlns:nc="http://nextcloud.org/ns">
	<d:response>
		<d:href>/server/remote.php/webdav/dsf/</d:href>
		<d:propstat>
			<d:prop>
				<d:resourcetype>
					<d:collection/>
				</d:resourcetype>
			</d:prop>
			<d:status>HTTP/1.1 200 OK</d:status>
		</d:propstat>
	</d:response>
	<d:response>
		<d:href>/server/remote.php/webdav/dsf/welcome.txt</d:href>
		<d:propstat>
			<d:prop>
				<d:resourcetype/>
			</d:prop>
			<d:status>HTTP/1.1 200 OK</d:status>
		</d:propstat>
	</d:response>
</d:multistatus>

@nickvergessen How to test this?

[nickvergessen]

nextcloud/server#5543 (comment)

Okay, seems like some other condition made this appear in 12+ so lets only fix it there...