fix #9411 - validator: no "crossing ways" warning for indoor ways with different `level`

git-svn-id: http://josm.openstreetmap.de/svn/trunk@6457 0c6e7542-c601-0410-84e7-c038aed88b3b
see #9411 - tagchecker: ignore `level` key

git-svn-id: http://josm.openstreetmap.de/svn/trunk@6458 0c6e7542-c601-0410-84e7-c038aed88b3b