On Windows RegEnumValueA() is buggy such that when the value name
buffer is too small, it may way overestimate the required data buffer
size, sometimes returning more than the sufficiently large buffer it was
provided, in which case that buffer is untouched and thus not
NUL-terminated.
So modify the tests to accept this broken result and avoid checking
out-of-bounds data.

Wine-Bug: https://bugs.winehq.org//show_bug.cgi?id=53172