Wrong deserialization for coproducts with empty lists

```scala
import pbdirect._

sealed trait Foo

case class Foo1(li: List[Int])
case class Foo2(ll: List[Long])
import cats.instances.list._

println(Foo1(List.empty).toPB.toSeq)
println(Foo2(List.empty).toPB.toSeq)

// prints
// WrappedArray()
// WrappedArray()
```

So in general `(a: A).toPb.pbTo[A] == a` can be false