Security: more cmsgpack fixes by @soloestoy.

@soloestoy sent me this additional fixes, after searching for similar
problems to the one reported in mp_pack(). I'm committing the changes
because it was not possible during to make a public PR to protect Redis
users and give Redis providers some time to patch their systems.
void *mp_realloc(lua_State *L, void *target, size_t osize,size_t nsize) {
    void *(*local_realloc) (void *, void *, size_t osize, size_t nsize) = NULL;
    void *ud;

    local_realloc = lua_getallocf(L, &ud);

    return local_realloc(ud, target, osize, nsize);
}

void *mp_realloc(lua_State *L, void *target, size_t osize,size_t nsize) {
    void *(*local_realloc) (void *, void *, size_t osize, size_t nsize) = NULL;
    void *ud;

    local_realloc = lua_getallocf(L, &ud);

    return local_realloc(ud, target, osize, nsize);
}
