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