Unmarshaling omits embedded pointer to an aliased primitive

[ericklaus-wf]

Related to #362

When unmarshaling a struct with an embedded pointer to an aliased primitive, the resulting struct omits the the pointer field leaving it nil.

The original struct is correctly serialized. For example, in the test below, the AliasedPrimitive field has a value of 7.

func TestIssue372(t *testing.T) {
	type AliasedPrimitive int
	type Combiner struct {
		SomeField int
		*AliasedPrimitive
	}
	aliasedPrimitive := AliasedPrimitive(7)
	originalCombiner := Combiner{AliasedPrimitive: &aliasedPrimitive}
	b, err := json.Marshal(originalCombiner)
	assertErr(t, err)
	newCombiner := Combiner{}
	err = json.Unmarshal(b, &newCombiner)
	assertErr(t, err)
	assertEq(t, "TestEmbeddedPrimitiveAlias", *originalCombiner.AliasedPrimitive, *newCombiner.AliasedPrimitive)
}

panics due to newCombiner.AliasedPrimitive being nil.