validator: fix potential infinite loop

[davidpanderson]

Fixes #5799

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 5 lines in your changes missing coverage. Please review.

Project coverage is 10.51%. Comparing base (29af35c) to head (266c050).
Report is 2 commits behind head on master.

Files with missing lines	Patch %	Lines
sched/validate_util2.cpp	0.00%	3 Missing ⚠️
sched/script_validator.cpp	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff            @@
##             master    #5813   +/-   ##
=========================================
  Coverage     10.51%   10.51%           
  Complexity     1068     1068           
=========================================
  Files           280      280           
  Lines         36021    36019    -2     
  Branches       8444     8444           
=========================================
  Hits           3789     3789           
+ Misses        31843    31841    -2     
  Partials        389      389           

Files with missing lines	Coverage Δ
sched/script_validator.cpp	0.00% <0.00%> (ø)
sched/validate_util2.cpp	0.00% <0.00%> (ø)