v2v:utils: ignore files w/o extension

When searching for virtio drivers, it makes no sense to fail if we
encounter a file without extension.

Ignore such files instead, just like we do for the files whose extension
doesn't match that of a driver-related file.

Signed-off-by: Roman Kagan <rkagan@virtuozzo.com>

v2v/utils.ml

@@ -238,9 +238,8 @@ let find_virtio_win_drivers virtio_win =
           let extension =
             match last_part_of lc_basename '.' with
             | Some x -> x
-            | None ->
-              error "v2v/find_virtio_win_drivers: missing '.' in %s"
-                lc_basename in
+            | None -> raise Not_found
+          in
 
           (* Skip files without specific extensions. *)
           if extension <> "cat" && extension <> "inf" &&