Motor Vehicle Safety and Financial Responsibility Act; multiple tortfeasors in collision between motorcycle and car, one underinsured and one uninsured; victim covered by two uninsured policies and one combined uninsured/underinsured policy; summary judgment in favor of insurance carrier; carrier not obligated to pay beyond combined limit of policy; carrier not entitled to a credit against its uninsured policy for payment from tortfeasor's liability coverage; bad faith refusal to settle and unfair trade practices