nir: handle negative array idx in lower_vars_to_ssa
Fixes: d477beab ("nir: Add a pass to lower local variable accesses to SSA values")
Possible fix for Emma's issue here !18466 (comment 1541817)
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Fixes: d477beab ("nir: Add a pass to lower local variable accesses to SSA values")
Possible fix for Emma's issue here !18466 (comment 1541817)