Add failing test for nil IsntanceState in State

A nil InstanceState within State/Modules/Resources/Deposed will panic
during a deep copy. The panic needs to be fixed in copystructure, but
the nil probably should have been normalized out before we got here too.

terraform/state_test.go

@@ -254,30 +254,64 @@ func TestStateModuleOrphans_deepNestedNilConfig(t *testing.T) {
 
 func TestStateDeepCopy(t *testing.T) {
 	cases := []struct {
-		One, Two *State
-		F        func(*State) interface{}
+		State *State
 	}{
 		// Version
 		{
 			&State{Version: 5},
-			&State{Version: 5},
-			func(s *State) interface{} { return s.Version },
 		},
-
 		// TFVersion
 		{
 			&State{TFVersion: "5"},
-			&State{TFVersion: "5"},
-			func(s *State) interface{} { return s.TFVersion },
+		},
+		// Modules
+		{
+			&State{
+				Version: 6,
+				Modules: []*ModuleState{
+					&ModuleState{
+						Path: rootModulePath,
+						Resources: map[string]*ResourceState{
+							"test_instance.foo": &ResourceState{
+								Primary: &InstanceState{
+									Meta: map[string]string{},
+								},
+							},
+						},
+					},
+				},
+			},
+		},
+		// Deposed
+		{
+			&State{
+				Version: 6,
+				Modules: []*ModuleState{
+					&ModuleState{
+						Path: rootModulePath,
+						Resources: map[string]*ResourceState{
+							"test_instance.foo": &ResourceState{
+								Primary: &InstanceState{
+									Meta: map[string]string{},
+								},
+								Deposed: []*InstanceState{
+									{ID: "test"},
+									nil,
+								},
+							},
+						},
+					},
+				},
+			},
 		},
 	}
 
 	for i, tc := range cases {
 		t.Run(fmt.Sprintf("copy-%d", i), func(t *testing.T) {
-			actual := tc.F(tc.One.DeepCopy())
-			expected := tc.F(tc.Two)
+			actual := tc.State.DeepCopy()
+			expected := tc.State
 			if !reflect.DeepEqual(actual, expected) {
-				t.Fatalf("Bad: %d\n\n%s\n\n%s", i, actual, expected)
+				t.Fatalf("Expected: %#v\nRecevied: %#v\n", expected, actual)
 			}
 		})
 	}