add step to simd_index

Author: johnnychen94

base/multidimensional.jl

@@ -432,7 +432,7 @@ module IteratorsMD
 
     simd_index(iter::CartesianIndices{0}, ::CartesianIndex, I1::Int) = first(iter)
     @inline function simd_index(iter::CartesianIndices, Ilast::CartesianIndex, I1::Int)
-        CartesianIndex((I1+first(iter.indices[1]), Ilast.I...))
+        CartesianIndex(getindex(iter.indices[1], I1+first(Base.axes1(iter.indices[1]))), Ilast.I...)
     end
 
     # Split out the first N elements of a tuple