changed if condition of rt_mat to be consistent with code

mmdet3d/core/bbox/structures/coord_3d_mode.py

@@ -243,9 +243,8 @@ def convert_point(point, src, dst, rt_mat=None):
                 f'Conversion from Coord3DMode {src} to {dst} '
                 'is not supported yet')
 
-        if isinstance(rt_mat, np.ndarray):
+        if not isinstance(rt_mat, torch.Tensor):
             rt_mat = arr.new_tensor(rt_mat)
-
         if rt_mat.size(1) == 4:
             extended_xyz = torch.cat(
                 [arr[:, :3], arr.new_ones(arr.size(0), 1)], dim=-1)