restrict _tryaxes to AbstractArrays since iterators would error

src/lib/array.jl

@@ -167,7 +167,7 @@ _reverse(x::Symmetric) = Symmetric(_reverse(x.data), x.uplo == 'U' ? :L : :U)
 
 # With mismatched lengths, map stops early. With mismatched shapes, it makes a vector.
 # So we keep axes(x) to restore gradient dx to its full length & correct shape.
-_tryaxes(x) = axes(x)
+_tryaxes(x::AbstractArray) = axes(x)
 _tryaxes(x::Tuple) = Val(length(x))
 _restore(dx, ax::Tuple) = axes(dx) == ax ? dx : reshape(vcat(dx, falses(prod(length, ax) - length(dx))), ax)
 _restore(dx, ::Val{N}) where {N} = ntuple(i -> get(dx,i,nothing), N)