[ISSUE #10873] fix(remoting): handle empty broker address tables

[yuluo-yx]

Which Issue(s) This PR Fixes

• Fixes [Bug] BrokerData.selectBrokerAddr crashes for an empty address table #10873

Brief Description

BrokerData.selectBrokerAddr now returns null when the address table is null or empty. Existing master preference and slave fallback behavior are unchanged and covered alongside the new boundary cases.

How Did You Test This Change?

• mise exec java@zulu-8.94.0.17 -- mvn -pl remoting -am -DskipITs -Dtest=BrokerDataTest -Dsurefire.failIfNoSpecifiedTests=false test (3 tests passed)
• Checkstyle and SpotBugs passed in the same Maven reactor.
• git diff --check and the 400-line scope gate passed.
• Not run: full repository build, container tests, or end-to-end tests.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 48.31%. Comparing base (fd0c959) to head (4d38a02).

Additional details and impacted files

@@              Coverage Diff              @@
##             develop   #10883      +/-   ##
=============================================
- Coverage      48.39%   48.31%   -0.09%     
+ Complexity     13562    13529      -33     
=============================================
  Files           1380     1380              
  Lines         101165   101167       +2     
  Branches       13127    13127              
=============================================
- Hits           48962    48881      -81     
- Misses         46233    46294      +61     
- Partials        5970     5992      +22     

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[RockteMQ-AI]

LGTM. Trivial change, looks good.

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