Tag return bifurcations too (#93)

Fixes a Revise `sigtest.jl` failure,
    LoadError: invalid redefinition of constant RandomDevice
on Windows with Julia 1.6.

src/codeedges.jl

@@ -769,8 +769,8 @@ function add_control_flow!(isrequired, cfg, paths::AbstractVector{Path})
         for (ibb, bb) in enumerate(blocks)
             r = rng(bb)
             if any(view(isrequired, r))
-                # Check if the exit of this block is a GotoNode
-                if length(bb.succs) == 1
+                # Check if the exit of this block is a GotoNode or `return`
+                if length(bb.succs) < 2 && ibb < nblocks
                     idxlast = r[end]
                     _changed |= !isrequired[idxlast]
                     isrequired[idxlast] = true