Fix sourceNodeClusterInfo.MigratingSlot maybe nil when tryUpdateMigrationStatus

[hll1213181368]

Fix sourceNodeClusterInfo.MigratingSlot maybe nil when tryUpdateMigrationStatus.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 0% with 14 lines in your changes missing coverage. Please review.
✅ Project coverage is 47.24%. Comparing base (6c56470) to head (bc72275).
⚠️ Report is 94 commits behind head on unstable.

Files with missing lines	Patch %	Lines
controller/cluster.go	0.00%	14 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##           unstable     #357      +/-   ##
============================================
+ Coverage     43.38%   47.24%   +3.86%     
============================================
  Files            37       45       +8     
  Lines          2971     4451    +1480     
============================================
+ Hits           1289     2103     +814     
- Misses         1544     2140     +596     
- Partials        138      208      +70     

Flag	Coverage Δ
unittests	47.24% <0.00%> (+3.86%)	⬆️

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

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[hll1213181368]

@git-hulk I have merge two if judgments, please review.

[git-hulk]

@hll1213181368 thank you!