Added a check for empty risk model files [skip hazardlib][demos]
Added a check for empty risk model files [skip hazardlib][demos]


Former-commit-id: c2e0e6b5fb78825fb67b9bbda6a3f06f312d0de5
gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine