nested message with default values regression

[kobykahane]

With the latest lua-protobuf master, the assertion on the last line of this program is hit:

pb = require 'pb'
protoc = require 'protoc'

assert(protoc:load[[
syntax = "proto3";

package repro;

message Inner {
    string value = 1;
}

message Outer {
    Inner inner = 1;
}
]])

outer = {inner={value=""}}

assert(outer)
assert(outer.inner)

m = assert(pb.decode('repro.Outer', assert(pb.encode('repro.Outer', outer))))

assert(m.inner, 'inner')

As follows:

lua5.4: repro.lua:25: inner
stack traceback:
        [C]: in function 'assert'
        repro.lua:25: in main chunk
        [C]: in ?

This does not happen with older versions of lua-protobuf. After a git bisect, I've narrowed the change in behavior down to commit 7de8652a02a19a421698e2cbf8c2460108552bf1. From the commit description, this change does not appear to be intentional.

[starwing]

This commit fix a encode bug, if you need default message, use option "decode_default_message"