Fix DX hang and added safety check

[Xelarse]

If using DX11 or DX12 on a machine with multiple graphics adapters (laptop with iGPU & dGPU) and the first adapter that EnumAdapters returns is the iGPU when OXR is expecting the dGPU; the application hangs infinitely. Mostly due to the oversight of forgetting to increment i each iteration of the while.

To prevent this hang entirely I've swapped the while out in favour of a for loop and added a small check underneath to throw if the adapter OXR wants isn't found by DX.

[CLAassistant]

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