fix: namespace_selector invalid when restarting

[AlinsRan]

Type of change:

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

What this PR does / why we need it:

• When all namespace do not have labels(namespace_selector), all resources will be monitored, and the namespace_selector function will not be available.
  

e2e-test:

• [un-label] When restarting, all ns without labels will be monitored
• [ingress-controller restart] When restarting, all ns without labels will be monitored

Pre-submission 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 #1238 (8d5b28c) into master (fcfa188) will decrease coverage by 0.13%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1238      +/-   ##
==========================================
- Coverage   42.78%   42.65%   -0.14%     
==========================================
  Files          73       73              
  Lines        6477     6478       +1     
==========================================
- Hits         2771     2763       -8     
- Misses       3409     3418       +9     
  Partials      297      297              

Impacted Files	Coverage Δ
pkg/api/validation/utils.go	32.43% <ø> (-12.02%)	⬇️
pkg/providers/apisix/translation/apisix_route.go	19.14% <0.00%> (-0.22%)	⬇️

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