[BUG] App is crashing if WebDAV server returns non-empty "getcontenttype" for a collection

Actual behaviour

Change WebDAV server to return a string for "getcontenttype" for a directory (collection) in the "200 OK" propstat for the resource, item of "getcontenttype" being in the "404 Not Found" propstat.

Refresh the file listing in the app. It crashes and cannot be restarted.

This works:

	<d:response>
		<d:href>/remote.php/webdav/Photos/</d:href>
		<d:propstat>
			<d:prop>
				<d:resourcetype>
					<d:collection/>
				</d:resourcetype>
				<d:getlastmodified>Mon, 03 Oct 2022 01:42:33 GMT</d:getlastmodified>
				<d:getetag>&quot;633a3e099376c&quot;</d:getetag>
				<d:quota-used-bytes>1011464</d:quota-used-bytes>
				<d:quota-available-bytes>-3</d:quota-available-bytes>
				<oc:permissions>RDNVCK</oc:permissions>
				<oc:id>00000013ocaveki6uxj5</oc:id>
				<oc:size>1011464</oc:size>
				<oc:privatelink>http://localhost:8082/index.php/f/13</oc:privatelink>
				<oc:share-types/>
			</d:prop>
			<d:status>HTTP/1.1 200 OK</d:status>
		</d:propstat>
		<d:propstat>
			<d:prop>
				<d:displayname/>
				<d:getcontenttype/>
				<d:getcontentlength/>
				<d:creationdate/>
			</d:prop>
			<d:status>HTTP/1.1 404 Not Found</d:status>
		</d:propstat>
	</d:response>

This makes the app crash:

	<d:response>
		<d:href>/remote.php/webdav/Photos/</d:href>
		<d:propstat>
			<d:prop>
				<d:resourcetype>
					<d:collection/>
				</d:resourcetype>
				<d:getlastmodified>Mon, 03 Oct 2022 01:42:33 GMT</d:getlastmodified>
				<d:getetag>&quot;633a3e099376c&quot;</d:getetag>
				<d:quota-used-bytes>1011464</d:quota-used-bytes>
				<d:quota-available-bytes>-3</d:quota-available-bytes>
				<oc:permissions>RDNVCK</oc:permissions>
				<oc:id>00000013ocaveki6uxj5</oc:id>
				<oc:size>1011464</oc:size>
				<oc:privatelink>http://localhost:8082/index.php/f/13</oc:privatelink>
				<oc:share-types/>
				<d:getcontenttype>something</d:getcontenttype>
			</d:prop>
			<d:status>HTTP/1.1 200 OK</d:status>
		</d:propstat>
		<d:propstat>
			<d:prop>
				<d:displayname/>
				<d:getcontentlength/>
				<d:creationdate/>
			</d:prop>
			<d:status>HTTP/1.1 404 Not Found</d:status>
		</d:propstat>
	</d:response>

Expected behaviour

No crash :)

Generally it seems that the app is very fragile if the WebDAV server response changes, even just a bit, more checks should be done instead of failing dramatically like that.

Start by reproducing the file-list refresh with the two WebDAV XML responses shown in the issue, then trace the crash through the app's WebDAV response handling. Done means the listing no longer crashes when a collection has a non-empty getcontenttype in a 200 OK propstat, while the existing response remains supported.