fix crash if some useless fields are missing in global form
fix crash if some useless fields are missing in global form

yannrouillard/weboob,sputnick-dev/weboob,laurent-george/weboob,Konubinix/weboob,willprice/weboob,Konubinix/weboob,frankrousseau/weboob,nojhan/weboob-devel,sputnick-dev/weboob,laurent-george/weboob,nojhan/weboob-devel,yannrouillard/weboob,yannrouillard/weboob,Konubinix/weboob,RouxRC/weboob,frankrousseau/weboob,willprice/weboob,Boussadia/weboob,sputnick-dev/weboob,willprice/weboob,RouxRC/weboob,Boussadia/weboob,Boussadia/weboob,RouxRC/weboob,Boussadia/weboob,laurent-george/weboob,nojhan/weboob-devel,frankrousseau/weboob