go/parser: valid conversion using a map type literal is rejected

[cznic]

This code (playgound)

package main

type t map[int]int

func main() {
    t := map[int]int{}
    map[int]int(t)[1] = 2
    println("ok")
}

compiles and runs ok, but clicking Format fails because go/parser reports

7:2: expected statement, found 'map' (and 1 more errors).

[minux]

Already fixed on tip.