fix out-of-bounds read in windows_read_manifest_from_d3d_adapters

[aizu-m]

Was reading why the D3D adapter path converts its registry strings differently to the rest of the loader, which is where this turned up.

1. json_path is sized to output_value_size, the UTF-16 byte length of the path.
2. the UTF-8 form can be longer, since a U+0800 to U+FFFF code point is 2 bytes in UTF-16 and 3 in UTF-8, so WideCharToMultiByte returns 0 and leaves json_path unterminated.
3. that return was ignored, so strlen(json_path) then walked off the end of the allocation.

Reachable from D3DKMT adapter data during driver and layer discovery. Every other WideCharToMultiByte call in the loader either queries the size first or checks the result. Took the return value as the length and skip the entry when it comes back 0.

[ci-tester-lunarg]

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[ci-tester-lunarg]

Author aizu-m not on autobuild list. Waiting for curator authorization before starting CI build.