Somehow the field is not present for sound capture devices, at least on my Win11.
Fixes Tom Clancy's Splinter Cell: Conviction not finding any sound devices and refusing to start.
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https://gitlab.winehq.org/wine/wine/-/merge_requests/6097
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v2: setupapi: Use SetupGetIntField() in SetupGetSourceFileLocation().
setupapi: Return the file's relative path from SetupGetSourceFileLocation().
setupapi: Correctly interpret the INFCONTEXT parameter in SetupGetSourceFileLocation().
setupapi/tests: Add more tests for SetupGetSourceFileLocation().
https://gitlab.winehq.org/wine/wine/-/merge_requests/6089