fix: correct type assertion for bin func types

[mvertes]

Fixes #587.

[derivaro]

Hello Marc, sorry if i m late to answer, lot of work....
I m trying to do a piece of code that i do everyday with goroutine, but with interpreted code (with yaegi) to be able to update it "on the fly" the code with a web site that store code snippets...
I do not use static types because json are differents everyday.

js1:=`{api_key:"testkey1", field2:"test2", products[{...}]}`
 var qq map[string]interface{}
  qq = make(map[string]interface{}, 20)
 if err := json.Unmarshal([]byte(js1), &qq); err != nil {

  }
//at this point no error detected and err==nil,
// but if i try to use the interface map qq :
	 apikey := qq["api_key"].(string)
fmt.Println(apikey)  //for example
//this crash yaegi and qq is not filled with the json

I m sure that the code works outside Yaegi.
It would be cool if u can fix this thing because i really love yaegi, it s very powerfull and very usefull (can code backend directly from front and other stranges features to build dynamic code ...)
Rgd
Antoine

[mvertes]

The unit test map25.go performs something close to what you claim, and works ok on master.
If something is wrong on your side, please could you provide a simple reproducible example like this test ? I can not guess what is not ok with what you provided.
Thanks.