Make iterate(::Number) more digestible by abstract_iteration

Letting the presence of a second argument alone decide whether iteration
is done lets `abstract_iteration` determine that splatting a `Number`
yields exactly one `Number`.

base/number.jl

@@ -233,7 +233,8 @@ julia> widemul(Float32(3.), 4.)
 """
 widemul(x::Number, y::Number) = widen(x)*widen(y)
 
-iterate(x::Number, done = false) = done ? nothing : (x, true)
+iterate(x::Number) = (x, nothing)
+iterate(x::Number, ::Any) = nothing
 isempty(x::Number) = false
 in(x::Number, y::Number) = x == y
 

test/core.jl

@@ -6235,3 +6235,8 @@ function f27597(y)
 end
 @test f27597([1]) == [1]
 @test f27597([]) == 1:0
+
+# issue #22291
+wrap22291(ind) = (ind...,)
+@test @inferred(wrap22291(1)) == (1,)
+@test @inferred(wrap22291((1, 2))) == (1, 2)