optimize: zk push empty protect

[laywin]

• [x] I have registered the PR changes.

Ⅰ. Describe what this PR did

https://github.com/apache/incubator-seata/issues/6162

Ⅱ. Does this pull request fix one issue?

fixes #6162

Ⅲ. Why don't you add test cases (unit test/integration test)?

Ⅳ. Describe how to verify it

Ⅴ. Special notes for reviews

[codecov-commenter]

Codecov Report

Attention: 5 lines in your changes are missing coverage. Please review.

Comparison is base (d2dbbff) 48.98% compared to head (63705fc) 49.02%.

Additional details and impacted files

@@             Coverage Diff              @@
##                2.x    #6206      +/-   ##
============================================
+ Coverage     48.98%   49.02%   +0.04%     
- Complexity     4779     4785       +6     
============================================
  Files           915      915              
  Lines         31896    31909      +13     
  Branches       3855     3856       +1     
============================================
+ Hits          15624    15644      +20     
+ Misses        14710    14705       -5     
+ Partials       1562     1560       -2     

Files	Coverage Δ
...very/registry/zk/ZookeeperRegisterServiceImpl.java	67.33% <75.00%> (+5.28%)	:arrow_up:

... and 3 files with indirect coverage changes