Fix bundling modules with early returns

[jeparlefrancais]

Bundling with modules that contains an early return causes a bug where the single file will also have the same early returns:

-- file A
do
    return "a"
end

return "b"

-- main
local A = require("A")

return { A = A }

So when bundling from main, darklua produces the incorrect code:

local __DARKLUA_BUNDLE_MODULES={}do do
    return "a"
end

__DARKLUA_BUNDLE_MODULES.a="b"
end

local A = __DARKLUA_BUNDLE_MODULES.a

return { A = A }