Add trailing periods support to `FindFirstFileA`

[AngheloAlf]

Adds support to handle directories with trailing periods (ie include/.) passed to FindFirstFileA and family.

I couldn't find docs on how the function should behave in this case (https://learn.microsoft.com/en-us/windows/win32/api/fileapi/nf-fileapi-findfirstfilea), but assuming it means "find anything on the passed directory" makes the program happy.

This was needed by "GCC 2.95.3 SN 1.14's cpp.exe"

I also added an assert in FindFirstFileA to check for wildcards and a few other unrelated logs. I can remove them if preferred.

[AngheloAlf]

Removed the wildcard assert since the CI test passes a wildcard to FindFirstFileA