ir.attachment: handle missing name from res_model
ir.attachment: handle missing name from res_model

If, for any reason, the related model cannot return sth through its
name_get, don't bork.

vnc-biz/openerp-server,gisce/openobject-server,gisce/openobject-server,splbio/openobject-server,MarkusTeufelberger/openobject-server,splbio/openobject-server,vnc-biz/openerp-server,ovnicraft/openerp-server,MarkusTeufelberger/openobject-server,MarkusTeufelberger/openobject-server,gisce/openobject-server,ovnicraft/openerp-server,splbio/openobject-server