fix int overflow

[AdrienTaylor]

Bug raised by @renaudgaucher and overflow identified by @bgoujaud

[codecov]

Codecov Report

❌ Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 89.11%. Comparing base (fb1941f) to head (3d52281).
⚠️ Report is 20 commits behind head on master.

Files with missing lines	Patch %	Lines
PEPit/wrappers/mosek_wrapper.py	0.00%	2 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #124   +/-   ##
=======================================
  Coverage   89.11%   89.11%           
=======================================
  Files         195      195           
  Lines        7421     7421           
=======================================
  Hits         6613     6613           
  Misses        808      808           

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