winpr: fix PathCchAppend

winpr: fix PathCchAppend

Fix incorrect usage of S_FALSE which was used to indicate errors
although it is a HRESULT success code.
Make this function behave like the Windows 8 implementation and
the according MSDN specification.

- return E_INVALIDARG instead of S_FALSE if pszPath is NULL
- return E_INVALIDARG instead of S_FALSE if pszMore is NULL
- return E_INVALIDARG if cchPath is zero
- return E_INVALIDARG if cchPath is greater than PATHCCH_MAX_CCH
- return HRESULT_FROM_WIN32(ERROR_FILENAME_EXCED_RANGE) if the combined
  path size exceeds cchPath (this is the same HRESULT which the Windows
  implementation returns in this case and which is referred to as
  PATHCCH_E_FILENAME_TOO_LONG on msdn)

Also extended/fixed the TestPathCchAppend ctest