fix empty slice is converted to nil in un ConvertibleTo case

[hhh111119]

fix an empty slice is converted to nil issue. could check the test case add by me.

func TestEmptySlice(t *testing.T) {
	type Str1 string
	type Str2 string
	type Input1 struct {
		Val Str1
	}
	type Input2 struct {
		Val Str2
	}
	to := []*Input1(nil)
	from := []*Input2{}
	err := copier.Copy(&to, &from)
	if err != nil {
		t.Error("should not error")
	}
	if from == nil {
		t.Error("from should be empty slice not nil")
	}

	to = []*Input1(nil)
	from = []*Input2(nil)
	err = copier.Copy(&to, &from)
	if err != nil {
		t.Error("should not error")
	}
	if from != nil {
		t.Error("from should be empty slice nil")
	}
}

[archiewx]

Why not release a new version of pkg