[Rock-dev] envire grid writing of bands

[Jakob Schwendner]

Currently in envire/maps/Grid.hpp, the behaviour for serializing any 
grid is to write all bands registered with the gridtype, regardless of 
whether they exist in the object or not. I will change that to only 
writing bands that actually do exist in the object, unless there is some 
form of resistance from anyone (which will be futile of course :) ).

cheers,

Jakob