CardDAV: "--status target-config@" aborts (FDO #56263)

"--status target-config@..." cannot really report on the status of the target
side of the sync, because nothing in the command line identifies *which* sync
is meant to be reported on: the same target config can be used in multiple
sync configs, therefore the meta data which tracks changes is attached to the
sync config, not the target config.

It should not abort, though, which happened because the backend had not
been properly initialized in this particular code path. Now it reports
the total number of items and zero changes.

Long term a dedicated error message would be better (see FDO #57145).

src/backends/webdav/WebDAVSource.cpp

@@ -1293,6 +1293,8 @@ static const ne_propname getetag[] = {
 
 void WebDAVSource::listAllItems(RevisionMap_t &revisions)
 {
+    contactServer();
+
     if (!getContentMixed()) {
         // Can use simple PROPFIND because we do not have to
         // double-check that each item really contains the right data.