fix(line): Line Charts do not work when lte is set to null

[likexin-kk]

Brief Information

This pull request is in the type of:

• bug fixing
• new feature
• others

What does this PR do?

fix: #18066

Fixed issues

#18066

Details

Before: What was the problem?

Set visualMap.pieces[].lte to null

1. Uncaught TypeError: Cannot read properties of undefined (reading 'coord')
2. Color should applied from 0 to max value.

After: How does it behave after the fixing?

1. No error reported
2. Color ranges from 0 to maximum value.

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

N.A.

Others

Merging options

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

Other information

[echarts-bot]

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