[loader] Exit if execv failed

[iamluc]

Description

if execv fails, we must exit immediately

Reviewer checklist

• Test coverage seems ok.
• Appropriate labels assigned.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 74.82%. Comparing base (34baa56) to head (ec7518a).

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #2983      +/-   ##
============================================
+ Coverage     73.12%   74.82%   +1.70%     
  Complexity     2741     2741              
============================================
  Files           137      110      -27     
  Lines         14907    10863    -4044     
  Branches        992        0     -992     
============================================
- Hits          10900     8128    -2772     
+ Misses         3462     2735     -727     
+ Partials        545        0     -545     

Flag	Coverage Δ
appsec-extension	?
tracer-php	74.82% <ø> (ø)

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see 27 files with indirect coverage changes

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