Added a check on self.prefilter_sources for preclassical [skip CI]
Added a check on self.prefilter_sources for preclassical [skip CI]


Former-commit-id: 98088f5ef1f841bcdf79bdd02ad622ca068b4e75
gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine