[bug] mixed notation of objects  with { } and . lead to null

minimal repro:
```scala
  @Test
  def parseNestedObjectsWithMixedNotations() = {
    val config = ConfigFactory.parseString("a { b.c { d = 1 } }")

    assert { config != null }

    assertEquals(config.getConfig("a.b.c").getInt("d"), 1)
  }
```
this will fail throwing a NPE