If a disease is unknown, return 404 Addresses issue #441
If a disease is unknown, return 404
Addresses issue #441

jmcmurry/monarch-app,DoctorBud/monarch-app,kshefchek/monarch-app,kshefchek/monarch-app,jmcmurry/monarch-app,monarch-initiative/monarch-app,monarch-initiative/monarch-app,monarch-initiative/monarch-app,jmcmurry/monarch-app,monarch-initiative/monarch-app,jmcmurry/monarch-app,kshefchek/monarch-app,DoctorBud/monarch-app,jmcmurry/monarch-app,monarch-initiative/monarch-app,kshefchek/monarch-app,DoctorBud/monarch-app,kshefchek/monarch-app,DoctorBud/monarch-app,DoctorBud/monarch-app