BUG/MINOR: hlua/init: coroutine may not resume itself

BUG/MINOR: hlua/init: coroutine may not resume itself

It's not supported to call lua_resume with <L> and <from> designating
the same lua coroutine. It didn't cause visible bugs so far because
Lua 5.3 used to be more permissive about this, and moreover, yielding
is not involved during the hlua init state.

But this is wrong usage, and the doc clearly specifies that the <from>
argument can be NULL when there is no such coroutine, which is the case
here.

This should be backported in every stable versions.