fix(pie): fix labelLine NPE when minShowLabelRadian is set

[plainheart]

Brief Information

This pull request is in the type of:

• bug fixing
• new feature
• others

What does this PR do?

Fix an undefined error of labelLine when the sector angle is less than minShowLabelRadian.
This bug was unexpectedly brought by #17412, which is in v5.4.0.

Fixed issues

• Resolves [Bug] Pie chart: minShowLabelAngle and label.position break down together #17712

Details

Before: What was the problem?

After: How does it behave after the fixing?

Document Info

One of the following should be checked.

• This PR doesn't relate to document changes
• The document should be updated later
• The document changes have been made in apache/echarts-doc#xxx

Misc

ZRender Changes

• This PR depends on ZRender changes (ecomfe/zrender#xxx).

Related test cases or examples to use the new APIs

Please refer to the last case in test/pie-label.html

Others

Merging options

• Please squash the commits into a single one when merging.

Other information

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[echarts-bot]

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