go/format: turns correct program into incorrect one

[dvyukov]

go fmt changed the following correct Go program:

package main

func main() {
    x := 0 /**/; y := 1
    _, _ = x, y
}

into the following incorrect Go program:

package main

func main() {
    x := 0 /**/ y := 1
    _, _ = x, y
}

[griesemer]

Should probably be fixed but is not urgent. This bug has been around for years.