Fix crash during initial skill download
Fix crash during initial skill download

When running on a platform for which there was not DEFAULT.platform
file in the mycroft-skills repo, the downloading of skills would
crash.  Now an informational message is shown and the DEFAULT
skills alone are loaded.

Dark5ide/mycroft-core,linuxipho/mycroft-core,Dark5ide/mycroft-core,MycroftAI/mycroft-core,MycroftAI/mycroft-core,linuxipho/mycroft-core,forslund/mycroft-core,forslund/mycroft-core