fix nil pointer

[nicktming]

What this PR does:
fix some nil pointer

Which issue(s) this PR fixes:

Fixes #

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

[codecov-commenter]

Codecov Report

Merging #517 (e69abd3) into develop (8dc4bd6) will decrease coverage by 0.03%.
The diff coverage is 0.00%.

@@             Coverage Diff             @@
##           develop     #517      +/-   ##
===========================================
- Coverage    54.70%   54.67%   -0.04%     
===========================================
  Files          666      666              
  Lines        77864    77865       +1     
===========================================
- Hits         42596    42569      -27     
- Misses       31631    31653      +22     
- Partials      3637     3643       +6     

Impacted Files	Coverage Δ
pixiu/pkg/config/config_load.go	44.53% <0.00%> (-0.38%)	⬇️
pilot/pkg/serviceregistry/kube/controller/sync.go	75.00% <0.00%> (-25.00%)	⬇️
pkg/config/mesh/kubemesh/watcher.go	59.01% <0.00%> (-11.48%)	⬇️
pkg/kube/inject/watcher.go	48.14% <0.00%> (-8.65%)	⬇️
pkg/kube/controllers/queue.go	55.22% <0.00%> (-7.47%)	⬇️
pkg/istio-agent/xds_proxy_delta.go	46.11% <0.00%> (-5.70%)	⬇️
pilot/pkg/model/addressmap.go	63.23% <0.00%> (-4.42%)	⬇️
security/pkg/nodeagent/sds/sdsservice.go	84.76% <0.00%> (-2.65%)	⬇️
pilot/pkg/xds/adstest.go	66.66% <0.00%> (-1.52%)	⬇️
.../pkg/serviceregistry/kube/controller/controller.go	71.92% <0.00%> (-0.61%)	⬇️
... and 10 more

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