Panic when walking nil pointer in struct field.

[ChrisHines]

To reproduce, modify the TestWalk_Struct test to this

func TestWalk_Struct(t *testing.T) {
    w := new(TestStructWalker)

    type S struct {
        Foo string
        Bar string
        Baz *int
    }

    data := &S{
        Foo: "foo",
        Bar: "bar",
    }

    err := Walk(data, w)
    if err != nil {
        t.Fatalf("err: %s", err)
    }

    expected := []string{"Foo", "Bar", "Baz"}
    if !reflect.DeepEqual(w.Fields, expected) {
        t.Fatalf("bad: %#v", w.Fields)
    }
}

Then run go test and observe the output:

--- FAIL: TestWalk_Struct (0.00s)
panic: unsupported type: invalid [recovered]
        panic: unsupported type: invalid

goroutine 14 [running]:
testing.func·006()
        c:/go/src/testing/testing.go:441 +0x188
github.com/mitchellh/reflectwalk.walk(0x0, 0x0, 0x0, 0x543c60, 0xc0820049a0, 0x0, 0x0)
        C:/gopath/src/github.com/mitchellh/reflectwalk/reflectwalk.go:159 +0x478
github.com/mitchellh/reflectwalk.walkStruct(0x548c20, 0xc082060360, 0xd9, 0x543c60, 0xc0820049a0, 0x0, 0x0)
        C:/gopath/src/github.com/mitchellh/reflectwalk/reflectwalk.go:294 +0x451
github.com/mitchellh/reflectwalk.walk(0x548c20, 0xc082060360, 0xd9, 0x543c60, 0xc0820049a0, 0x0, 0x0)
        C:/gopath/src/github.com/mitchellh/reflectwalk/reflectwalk.go:148 +0x5b1
github.com/mitchellh/reflectwalk.Walk(0x500a40, 0xc082060360, 0x543c60, 0xc0820049a0, 0x0, 0x0)
        C:/gopath/src/github.com/mitchellh/reflectwalk/reflectwalk.go:82 +0x13e
github.com/mitchellh/reflectwalk.TestWalk_Struct(0xc0820105a0)
        C:/gopath/src/github.com/mitchellh/reflectwalk/reflectwalk_test.go:369 +0xd4
testing.tRunner(0xc0820105a0, 0x62cd98)
        c:/go/src/testing/testing.go:447 +0xc6
created by testing.RunTests
        c:/go/src/testing/testing.go:555 +0xa92

[mitchellh]

Not sure when it was fixed but your test now passes on master :) We've done a lot of work to reflectwalk so it should be a lot more robust now!