feat(api): clear a WAF list when it cannot be deleted

[favonia]

Close #893.

[codecov]

Codecov Report

Attention: Patch coverage is 98.55596% with 4 lines in your changes missing coverage. Please review.

Project coverage is 95.59%. Comparing base (d7b917b) to head (57e57fa).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
cmd/ddns/ddns.go	0.00%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #908      +/-   ##
==========================================
+ Coverage   95.50%   95.59%   +0.08%     
==========================================
  Files          59       61       +2     
  Lines        2535     2586      +51     
==========================================
+ Hits         2421     2472      +51     
  Misses        104      104              
  Partials       10       10              

Flag	Coverage Δ
unittests	95.59% <98.55%> (+0.08%)	⬆️

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