Windows OpenXR Loader will silently ignore API layers upon parsing a bad registry key

When loading the list of API layers from `HKEY_LOCAL_MACHINE\SOFTWARE\Khronos\OpenXR\1\ApiLayers\Implicit`, the OpenXR loader will silently fail upon parsing a bad key. This can be reproduced by doing the following:

1) Add a DWORD key for API Layer number 1
2) Add a REG_SZ key (bad key)
3) Add a DWORD key for API Layer number 2

API Layer number 2 will not be loaded, but no error message is emitted (checked with both VS debugger and DebugView). This can cause very troublesome situations for API layer developers, especially when the "bad key" in question is the (Default) key not being set to an empty value (because that key is largely invisible to the naked eye).

Start by reproducing the registry setup described for HKEY_LOCAL_MACHINE\SOFTWARE\Khronos\OpenXR\1\ApiLayers\Implicit, then locate the Windows API-layer registry loading path. Verify how a malformed value affects later numbered layers and diagnostics; done means the valid later layer is still handled and the malformed entry is reported, with regression coverage.

Written by the indexing model from the issue text.