可视化部分draw_in_poincare_ball(), Norm 运算产生0，导致除法运算报错

[FUNCTIONair-han]

Describe the bug A clear and concise description of what the bug is.

To Reproduce Steps to reproduce the behavior:

1. Go to '...'
2. Click on '....'
3. Scroll down to '....'
4. See error

Expected behavior A clear and concise description of what you expected to happen.

Screenshots

Environment (please complete the following information):

• OS: [e.g. Ubuntu 18.04]
• Python: [e.g. 3.8.13]
• PyTorch [e.g. 1.11.0]
• DHG [e.g. 0.9.1]

Additional context Add any other context about the problem here.

[yifanfeng97]

Got it!