Make binary search overflow safe.
Make binary search overflow safe.

Our internal static analysis flags potentially unsafe midpoint
calculations. The proposed fix ensures the binary search doesn't
overflow at the cost of a single additional operation.

GPUOpen-LibrariesAndSDKs/VulkanMemoryAllocator,GPUOpen-LibrariesAndSDKs/VulkanMemoryAllocator,GPUOpen-LibrariesAndSDKs/VulkanMemoryAllocator