Fix bug in MHD initial conditions
Fix bug in MHD initial conditions

The last face wasn't being properly assigned, it's now been added to
the main assignment loop with guards to keep from setting hydro values

evaneschneider/cholla,cholla-hydro/cholla,evaneschneider/cholla,evaneschneider/cholla,cholla-hydro/cholla,cholla-hydro/cholla,evaneschneider/cholla,cholla-hydro/cholla