Fix sizeBytesToRequest in case if no request has been done

[UgnineSirdis]

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 1 line in your changes missing coverage. Please review.

Project coverage is 44.37%. Comparing base (ef49df2) to head (2e20069).

Files	Patch %	Lines
...main/java/tech/ydb/topic/read/impl/ReaderImpl.java	0.00%	1 Missing :warning:

Additional details and impacted files

@@             Coverage Diff              @@
##             master     #279      +/-   ##
============================================
- Coverage     44.39%   44.37%   -0.03%     
  Complexity     1571     1571              
============================================
  Files           297      297              
  Lines         11505    11506       +1     
  Branches       1124     1124              
============================================
- Hits           5108     5106       -2     
- Misses         5988     5991       +3     
  Partials        409      409              

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