Pointclouds.subsample on Windows

Summary: Fix https://github.com/facebookresearch/pytorch3d/issues/1015. Stop relying on the fact that the dtype returned by np.random.choice (int64 on Linux, int32 on Windows) matches the dtype used by pytorch for indexing (int64 everywhere).

Reviewed By: patricklabatut

Differential Revision: D33428680

fbshipit-source-id: 716c857502cd54c563cb256f0eaca7dccd535c10

pytorch3d/structures/pointclouds.py

@@ -891,7 +891,7 @@ class Pointclouds:
         ):
             if n_points > max_:
                 keep_np = np.random.choice(n_points, max_, replace=False)
-                keep = torch.tensor(keep_np).to(points.device)
+                keep = torch.tensor(keep_np, device=points.device, dtype=torch.int64)
                 points = points[keep]
                 if features is not None:
                     features = features[keep]