Fixed oq plot_sites in absence of rtree [skip CI]
Fixed oq plot_sites in absence of rtree [skip CI]


Former-commit-id: 24c8684a11b01b8d6aa1d82cd5aa9be356f9f67d [formerly aa78dedb1cfcf11e1b4927503405e23d18ce2434]
Former-commit-id: 21d6c65344665130f0deeedf3e7230ae50215ae4
gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine