Applying a complex in-place plan via '*' to a real vector should throw

[j-fu]

My colleague sent me this MWE - it is about defining a complex in-place plan.
This should mutate vectors when applied via '*' as documented.
When applying this to a vector of floats it should throw, but in fact it
returns a complex vector but does not mutate the the vector.

using FFTW

plan = plan_fft!(zeros(ComplexF64, 4))
vec1 = ComplexF64[1,1,1,1]
vec2 = [1,1,1,1]

# changes vec1 as expected
plan * vec1; println(vec1,"\n")

# sends error as expected
try
    FFTW.mul!(vec2, plan, vec2)
catch e;
    println(e,"\n")
end

# does not say anything and does not change vec2
plan * vec2; println(vec2,"\n")

PR follows.

[stevengj]

Seems reasonable.