conj() not correctly implemented for sparse complex matrices

[ntezak]

Element-wise complex conjugation is not supported for sparse matrices.
The following code should result in a single element sparse matrix with value 0im

conj(sparse([1im])) - sparse(conj([1im])) 
# should be sparse([0im]), but returns sparse([2im])

I think this used to be correctly defined but must have been broken recently.
I've added a pull request (issue #8977 )

[ViralBShah]

This is the problem:

julia> @which conj(sparse([1im]))
conj(x) at operators.jl:141

[ntezak]

thanks!