combine: fix directory not found errors with ListP interface - Fixes #8627

In

b1d774c2e3 combine: implement ListP interface

We introduced the ListP interface to the combine backend. This was
passing the wrong remote to the upstreams. This was picked up by the
integration tests but was ignored by accident.

backend/combine/combine.go

@@ -858,7 +858,7 @@ func (f *Fs) ListP(ctx context.Context, dir string, callback fs.ListRCallback) e
 		}
 		return wrappedCallback(entries)
 	}
-	return listP(ctx, dir, wrappedCallback)
+	return listP(ctx, uRemote, wrappedCallback)
 }
 
 // ListR lists the objects and directories of the Fs starting