use the attribute am_l_obj for Oject Nr

Wrong attribute use for Object Nr 
Ticket 2382 in redmine.

URL de test : http://mf-chsdi3.dev.bgdi.ch/ltalp/rest/services/ech/MapServer/ch.bafu.bundesinventare-amphibien/1578/htmlPopup?imageDisplay=1369,892,96&lang=en&mapExtent=434896.4154515237,95127.88446737794,571796.4154515236,184327.88446737794