Describe the bug
On D3D12, creating more than 64 samplers will throw an exception in DescriptorAllocatorD3D12::alloc() on line device->CreateSampler(&sd, cpuHandle);

To Reproduce
Steps to reproduce the behavior:

1. Create at least 65 different texture samplers
2. Launch with D3D12 renderer
3. See error

I've forked and edited example 6-bump to reproduce the issue (https://github.com/falia18/bgfx/tree/d3d12-sampler-crash-example)
Clone the project and switch to branch d3d12-sampler-crash-example
Launch example 6-bump with --d3d12 and crash will occur after ~20 frames.

Expected behavior
Sampler creation proceeds without exception.

Additional context
Tested on Windows 10 with both NVIDIA and AMD GPU