And again S_FALSE was incorrectly used to indicate an error.
Fix this and be more compatible to the Windows 8 implementation of
this function:
- return E_INVALIDARG instead of S_FALSE if pszPath is NULL
- return E_INVALIDARG instead of S_FALSE if cchPath < 4
- return E_INVALIDARG if cchPath > PATHCCH_MAX_CCH
- allow stripping of "\\?\c:" and don't require "\\?\c:\"
- verify that the character at the drive letter position is
actually an alphabetic character
- since the passed pszPath must not necessarily be null terminated
and we always have enough space after the memmove we can always
ensure the null termination of the stripped result
Also extended/fixed the TestPathCchStripPrefixctest
