Fix plot for 1.6

[sylee957]

References to other Issues or PRs

Brief description of what is fixed or changed

#19252 for 1.6 branch

Other comments

Release Notes

• plotting
  • Fixed plot3d_parametric_line plotting curves out of the box.

[sympy-bot]

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• plotting
  • Fixed plot3d_parametric_line plotting curves out of the box. (#19284 by @sylee957)

This will be added to https://github.com/sympy/sympy/wiki/Release-Notes-for-1.6.

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#### References to other Issues or PRs
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#### Brief description of what is fixed or changed

#19252 for 1.6 branch

#### Other comments


#### Release Notes

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<!-- BEGIN RELEASE NOTES -->
- plotting
  - Fixed plot3d_parametric_line plotting curves out of the box.
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Update

The release notes on the wiki have been updated.

[oscarbenjamin]

Thanks @sylee957 for the quick work on this

[codecov]

Codecov Report

Merging #19284 into 1.6 will decrease coverage by 0.029%.
The diff coverage is 23.711%.

@@              Coverage Diff              @@
##               1.6    #19284       +/-   ##
=============================================
- Coverage   75.678%   75.648%   -0.030%     
=============================================
  Files          651       651               
  Lines       169489    169528       +39     
  Branches     40021     40021               
=============================================
- Hits        128266    128246       -20     
- Misses       35612     35664       +52     
- Partials      5611      5618        +7     

[oscarbenjamin]

Thanks