Added ?'s in wms-string causes layers to error out when wmsSource is set

[giovanniborella]

Discussed in mapcentia/geocloud2#148

I have implemented a crude fix here https://github.com/geopartner/vidi/commit/ccb2d92b7adfefffef5ceca3d596bf1cec124a19

but i guess the problem is before this point.