Fix concurrent issues caused by accessing request after calling Send

[bogdandrutu]

This can happen when items are added to the memory queue and processed by the batcher in the same time with reading the number of items from this code.

Though our queue does not return error and still add the item unless the Context is cancelled, but likely because of a bug that does not work as expected, see #12282

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 91.31%. Comparing base (bbe9cb8) to head (bcd902d).
Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #12281      +/-   ##
==========================================
+ Coverage   91.27%   91.31%   +0.03%     
==========================================
  Files         466      465       -1     
  Lines       25583    25586       +3     
==========================================
+ Hits        23351    23363      +12     
+ Misses       1816     1806      -10     
- Partials      416      417       +1     

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[dmitryax]

I was actually looking into this particular problem yesterday. Thank you!