Repeated mysql_stmt_execute+mysql_store_result allocate increasingly more memory

Repeated mysql_stmt_execute+mysql_store_result allocate more and more memory,
This happens if the result set is more than approx. 4K in size

I'm attaching a reproducible test case
according to it, virtual memory use of the process grows from 1.5MB to almost 1GB after executing prepared "select repeat('a',5000)" statement 1 million times.

I think all versions are affected, even though the attached pull request is against 3.3