added validation for export multi curves
added validation for export multi curves


Former-commit-id: 65ea3cedcf7d227698a48d1ed9798b54334706fb [formerly 69c7b293426e94e5decc6d8fff74841f1f04e59d] [formerly 69c7b293426e94e5decc6d8fff74841f1f04e59d [formerly 3e7d3c5f73050a4a9ac78647edd4c7b141543309]]
Former-commit-id: 3c13f7ce683d38e8d28528aa129e8f35eb29d483
Former-commit-id: b03071e9df01d4d019c8dc735a3c9b87dc0003b5
gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine