Strange behavior with .elements on anonymous bundle

It seems that if you pass an anonymous bundle to a function without first assigning it to a val, reflection fails to find anything so its elements are empty.

```scala
import chisel3._

trait HasFoo { def foo: UInt }
class TestBundle extends Bundle with HasFoo {
val foo = UInt(32.W)
}

class TestModule extends Module {
val io = IO(new Bundle { })
def func(bun: Bundle): Unit = println(bun.elements)

// This one has empty elements!
func(new Bundle {
val foo = UInt(32.W)
})

func(new TestBundle)
func(new Bundle with HasFoo {
val foo = UInt(32.W)
})
func({
val b = new Bundle {
val foo = UInt(32.W)
}
b
})
}
```

This prints the following:
```scala
Map()
Map(foo -> chisel3.core.UInt@9)
Map(foo -> chisel3.core.UInt@b)
Map(foo -> chisel3.core.UInt@d)
```