[Cleanup] Add empty judgment for placement in taint-manager

[XiShanYongYe-Chang]

What type of PR is this?

/kind cleanup

What this PR does / why we need it:

1. Add empty judgment for placement in taint-manager, avoid panic when the obtained placement is nil:
   

   karmada/pkg/controllers/cluster/taint_manager.go

   Line 267 in 90b4616

   tolerations := placement.ClusterTolerations

2. Add more logs to facilitate fault locating.

Which issue(s) this PR fixes:
Fixes #

Special notes for your reviewer:

In order to make the program more robust, nil judgment is added.

This is because when users define their own scheduler, the placement recorded in the annotation in the binding may be empty.

Does this PR introduce a user-facing change?:

NONE

[XiShanYongYe-Chang]

/cc @GitHubxsy @RainbowMango

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 4 lines in your changes are missing coverage. Please review.

Project coverage is 53.22%. Comparing base (90b4616) to head (6bf87d0).

Files	Patch %	Lines
...acefuleviction/crb_graceful_eviction_controller.go	0.00%	2 Missing ⚠️
...racefuleviction/rb_graceful_eviction_controller.go	0.00%	2 Missing ⚠️

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Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4959      +/-   ##
==========================================
- Coverage   53.25%   53.22%   -0.03%     
==========================================
  Files         252      252              
  Lines       20514    20518       +4     
==========================================
- Hits        10925    10921       -4     
- Misses       8866     8873       +7     
- Partials      723      724       +1     

Flag	Coverage Δ
unittests	53.22% <0.00%> (-0.03%)	⬇️

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[RainbowMango]

You have to wait #4966

[RainbowMango]

/lgtm
/approve

[karmada-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: RainbowMango

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• pkg/controllers/OWNERS [RainbowMango]

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