Refcount leak in generator function

[bnoordhuis]

Refs: bellard/quickjs#394

function* f(r){ return r } // must return r
[...f({})]

r's ref count in async_func_free is 2, not 1.

f's bytecode looks like this:

;; function* f(r){ return r }      
                                                                               
        initial_yield                                                          
        get_arg0        0    ; r
        return_async       

The async stack frame at time of free looks like this: [r, undefined] (where slot 0 is arg 0); I suspect it should be [r, r] because then the ref counts would match up.

[saghul]

bellard/quickjs@0d7aaed