Gracefully handle case where gripper pointcloud has size 0

[hello-amal]

Description

If the gripper's pointcloud had depth 0 while gripper depth AR were enabled , it would crash. This PR addresses that.

Testing procedure

• Verify the fix: Before the changed code in configure_video_streams and move_to_pregrasp, add lines of code hardcoding the pointcloud size to 0 (e.g., np.zeros((0,3), dtype=np.uint16)). Launch the interface, toggle on gripper depth AR, try move-to-pregrasp, verify that the node doesn't crash.
• Remove those lines, try the above two features, verify that they work.

Before opening a pull request

From the top-level of this repository, run:

• pre-commit run --all-files

To merge

• Squash & Merge