[CBRD-24028] Segment fault occurs when connections increase rapidly

[shparkcubrid]

http://jira.cubrid.org/browse/CBRD-24028

When the number of inputs becomes larger than the size of m_stack, m_ext_block is used. But it does not copy the old value of m_stack into m_ext_block. This means there are garbage values.
I fix to copy data from m_stack to m_ext_block at first extension.

[codecov-commenter]

Codecov Report

Merging #2978 (d315673) into develop (423d5ca) will decrease coverage by 2.63%.
The diff coverage is 0.00%.

❗ Current head d315673 differs from pull request most recent head 3c22cca. Consider uploading reports for the commit 3c22cca to get more accurate results

@@             Coverage Diff             @@
##           develop    #2978      +/-   ##
===========================================
- Coverage    51.66%   49.03%   -2.64%     
===========================================
  Files          494      494              
  Lines       390170   388884    -1286     
===========================================
- Hits        201588   190686   -10902     
- Misses      188582   198198    +9616     

Impacted Files	Coverage Δ
src/base/mem_block.hpp	73.58% <0.00%> (-2.89%)	⬇️
src/loaddb/load_common.hpp	0.00% <0.00%> (-100.00%)	⬇️
src/loaddb/load_sa_loader.hpp	0.00% <0.00%> (-100.00%)	⬇️
src/loaddb/load_driver.cpp	0.00% <0.00%> (-81.82%)	⬇️
src/loaddb/load_semantic_helper.cpp	0.00% <0.00%> (-77.69%)	⬇️
src/loaddb/load_object_table.c	0.00% <0.00%> (-72.28%)	⬇️
src/base/base64.c	0.00% <0.00%> (-71.08%)	⬇️
src/loaddb/load_scanner.hpp	0.00% <0.00%> (-70.00%)	⬇️
src/query/query_method.c	0.00% <0.00%> (-56.25%)	⬇️
src/parser/method_transform.c	14.36% <0.00%> (-51.35%)	⬇️
... and 187 more

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