fixed wms group layer loading
fixed wms group layer loading

--HG--
branch : 0.9.1.x
extra : transplant_source : %8E%91%5C%F3%F6%EAC%10%8A%A8%3A%B5%A0%80U%F4%26%BF%2C%C2

geoadmin/mapproxy,faegi/mapproxy,drnextgis/mapproxy,camptocamp/mapproxy,drnextgis/mapproxy,kaiCu/mapproxy,procrastinatio/mapproxy,procrastinatio/mapproxy,Anderson0026/mapproxy,kaiCu/mapproxy,geoadmin/mapproxy,olt/mapproxy,olt/mapproxy,vrsource/mapproxy,Anderson0026/mapproxy,vrsource/mapproxy,mapproxy/mapproxy,faegi/mapproxy,camptocamp/mapproxy,mapproxy/mapproxy