[#4051]fix buffer reader not correct when length is 0

[liubao68]

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[codecov-commenter]

Codecov Report

Attention: 1 lines in your changes are missing coverage. Please review.

Comparison is base (3ccd557) 74.17% compared to head (9cf67e5) 74.17%.

❗ Current head 9cf67e5 differs from pull request most recent head 6dc253c. Consider uploading reports for the commit 6dc253c to get more accurate results

Files	Patch %	Lines
...omb/foundation/vertx/stream/BufferInputStream.java	80.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##              2.8.x    #4099      +/-   ##
============================================
- Coverage     74.17%   74.17%   -0.01%     
  Complexity      707      707              
============================================
  Files          1594     1594              
  Lines         40142    40144       +2     
  Branches       3655     3656       +1     
============================================
- Hits          29777    29775       -2     
- Misses         8883     8886       +3     
- Partials       1482     1483       +1     

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