fix: consumer without plugins causes page crashes

[qihaiyan]

Please answer these questions before submitting a pull request, or your PR will get closed.

Why submit this pull request?

• Bugfix
• New feature provided
• Improve performance
• Backport patches

What changes will this PR take into?

if a consoumer is created with admin api, and having no plugin param, the comsumer list page in dashbord would report error.
the reason is the 62 line in 'web/src/pages/Consumer/List.tsx' file doesn't check if record.plugins is null or undefined.

Related issues

fix/resolve #2436

Checklist:

• Did you explain what problem does this PR solve? Or what new features have been added?
• Have you added corresponding test cases?
• Have you modified the corresponding document?
• Is this PR backward compatible? If it is not backward compatible, please discuss on the mailing list first

[codecov-commenter]

Codecov Report

Merging #2437 (e3b41d9) into master (0e6411f) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #2437   +/-   ##
=======================================
  Coverage   68.57%   68.57%           
=======================================
  Files         131      131           
  Lines        3427     3427           
  Branches      831      832    +1     
=======================================
  Hits         2350     2350           
  Misses       1077     1077           

Flag	Coverage Δ
frontend-e2e-test	68.57% <100.00%> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
web/src/pages/Consumer/List.tsx	88.88% <100.00%> (ø)

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