Fix SimbodyConfig.cmake.in
Fix SimbodyConfig.cmake.in

I was missing some of the cmake standard error handling

elkingtonmcb/simbody,elen4/simbody,chrisdembia/simbody,robojukie/simbody,simbody/simbody,scamille/simbody,Gjacquenot/simbody,scamille/simbody,chrisdembia/simbody,simbody/simbody,robojukie/simbody,Gjacquenot/simbody,elkingtonmcb/simbody,elkingtonmcb/simbody,robojukie/simbody,Gjacquenot/simbody,chrisdembia/simbody,scamille/simbody,elen4/simbody