Cygwin: fhandler_virtual: move fileid to path_conv member

Cygwin: fhandler_virtual: move fileid to path_conv member

Commit 80f722e97cf7 ("Cygwin: opendir(3): move ENOTDIR check into main
function") introduced a bug in fhandler_virtual handling.  While the
assertion that path_conv::check() already calls exists() and sets
FILE_ATTRIBUTE_DIRECTORY accordingly, the exists() function is called
on a fhandler_virtual object created for just this code snippet.  The
side effect of this is that the fileid member in the calling
fhandler_virtual object is not set after path_conv::check().

Move the fhandler_virtual::fileid member to path_conv::_virt_fileid
and create matching path_conv::virt_fileid() and fhandler_virtual::fileid()
methods.

Let path_conv::check() propagate the fileid set in the local
fhandler_virtual::exists() call to its own  _virt_fileid.

Use new fhandler_virtual::fileid() method throughout.

Fixes: 80f722e97cf7 ("Cygwin: opendir(3): move ENOTDIR check into main function")
Reported-by: Bruce Jerrick <bmj001@gmail.com>
Signed-off-by: Corinna Vinschen <corinna@vinschen.de>