Loop counter resetting must not result in unlimited unwinding

[tautschnig]

Loops with multiple entry points previously resulted in unlimited
unwinding as loop counters were wrongly being reset via edges leaving
one of the loops (and entering the other).

• Each commit message has a non-empty body, explaining why the change was made.
• n/a Methods or procedures I have added are documented, following the guidelines provided in CODING_STANDARD.md.
• n/a The feature or user visible behaviour I have added or modified has been documented in the User Guide in doc/cprover-manual/
• Regression or unit tests are included, or existing tests cover the modified code (in this case I have detailed which ones those are in the commit message).
• n/a My commit message includes data points confirming performance improvements (if claimed).
• My PR is restricted to a single feature or bugfix.
• n/a White-space or formatting changes outside the feature-related changed lines are in commits of their own.

[codecov]

Codecov Report

Merging #5870 (8330dd3) into develop (e969911) will decrease coverage by 0.00%.
The diff coverage is 89.55%.

@@             Coverage Diff             @@
##           develop    #5870      +/-   ##
===========================================
- Coverage    72.90%   72.90%   -0.01%     
===========================================
  Files         1423     1423              
  Lines       154216   154196      -20     
===========================================
- Hits        112428   112412      -16     
+ Misses       41788    41784       -4     

Impacted Files	Coverage Δ
src/analyses/global_may_alias.cpp	0.00% <0.00%> (ø)
src/analyses/uninitialized_domain.cpp	0.00% <0.00%> (ø)
src/goto-diff/change_impact.cpp	0.00% <ø> (ø)
src/goto-instrument/uninitialized.cpp	0.00% <0.00%> (ø)
src/goto-symex/auto_objects.cpp	21.95% <0.00%> (+0.52%)	⬆️
src/goto-symex/goto_symex.h	92.30% <ø> (ø)
src/goto-symex/symex_function_call.cpp	92.89% <50.00%> (+0.50%)	⬆️
src/goto-programs/goto_program.h	90.06% <80.00%> (+0.03%)	⬆️
jbmc/src/java_bytecode/remove_exceptions.cpp	95.58% <100.00%> (-0.03%)	⬇️
src/analyses/constant_propagator.cpp	94.26% <100.00%> (-0.02%)	⬇️
... and 19 more

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[martin-cs]

OK... I don't think I want to know what you were doing when you found this issue...