zdb broken due to erroneous code (openzfsonwindows#320)

Author: datacore-yash

ZFSin/zfs/module/zfs/vdev_file.c

@@ -322,7 +322,7 @@ vdev_file_open(vdev_t* vd, uint64_t* psize, uint64_t* max_psize,
 #ifdef _KERNEL
 	*max_psize = *psize = info.EndOfFile.QuadPart;
 #else
-	if(FileName[0] == '#')
+	if(vd->vdev_physpath && vd->vdev_physpath[0] == '#')
 		*max_psize = *psize = vd->vdev_win_length;
 	else {
 		zfs_file_getattr(&fp, &zfa);