Fix integer overflow

[artemgavrilov]

Fixes https://github.com/percona/pg_stat_monitor/issues/412

This PR fixes 3 integer overflow bugs, all of them covered with tests.

[it-percona-cla]

All committers have signed the CLA.

[codecov[bot]]

Codecov Report

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

Project coverage is 90.55%. Comparing base (3d84610) to head (b0c05ec). Report is 1 commits behind head on main.

Files	Patch %	Lines
pg_stat_monitor.c	0.00%	0 Missing and 1 partial :warning:

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #435   +/-   ##
=======================================
  Coverage   90.55%   90.55%           
=======================================
  Files           3        3           
  Lines        1271     1271           
  Branches       35       35           
=======================================
  Hits         1151     1151           
  Misses         98       98           
  Partials       22       22           

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[Naeem-Akhter]

@codeforall @hqakhtar @dutow @dAdAbird

Can one of your please review c code files changes in this PR?