Fix segfault in k-induction step case with nested loops

[tautschnig]

The original code assumed loop_head->condition() always contained the loop guard, but in nested loop scenarios, the loop structure can vary. The backedge might contain the condition instead, or the loop might be unconditional.

Also, when processing nested loops, modifying the outer loop's goto-program could invalidate iterators pointing to the inner loop, causing memory access violations.

Co-authored-by: Kiro autonomous agent

Fixes: #5357

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