[generator] Ignore types without names.

[jpobst]

Fixes: #835

Somehow Google has compiled firebase-firestore.aar to contain a class with a dollar sign in its name:

    <class
      abstract="false"
      deprecated="not deprecated"
      jni-extends="Ljava/lang/Object;"
      extends="java.lang.Object"
      extends-generic-aware="java.lang.Object"
      final="false"
      name="Document."
      jni-signature="Lcom/google/firebase/firestore/model/Document$;"
      source-file-name="Document.java"
      static="false"
      visibility="public" />

This causes an IndexOutOfRangeException for generator when it tries to parse Document. into a parent class name and nested class name.

  Unhandled Exception: (TaskId:666)
  System.IndexOutOfRangeException: Index was outside the bounds of the array. (TaskId:666)

    at MonoDroid.Generation.XmlApiImporter.CreateGenBaseSupport (System.Xml.Linq.XElement pkg, System.Xml.Linq.XElement elem, System.Boolean isInterface) [0x0021c] in <fc31e3500e9a44b181504040e11d2f7d>:0  (TaskId:666)
    at MonoDroid.Generation.XmlApiImporter.CreateClass (System.Xml.Linq.XElement pkg, System.Xml.Linq.XElement elem, 
    at MonoDroid.Generation.Parser.ParsePackage (System.Xml.Linq.XElement ns, System.Predicate`1[T] p) [0x00087] in 
    at MonoDroid.Generation.Parser.ParsePackage (System.Xml.Linq.XElement ns) [0x00000] in 
    at MonoDroid.Generation.Parser.Parse (System.Xml.Linq.XDocument doc, System.Collections.Generic.IEnumerable`1[T] fixups, 
    at MonoDroid.Generation.Parser.Parse (System.String filename, System.Collections.Generic.IEnumerable`1[T] fixups, 
    at Xamarin.Android.Binder.CodeGenerator.Run (Xamarin.Android.Binder.CodeGeneratorOptions options, 
    at Xamarin.Android.Binder.CodeGenerator.Run (Xamarin.Android.Binder.CodeGeneratorOptions options) [0x0001b] in 
    at Xamarin.Android.Binder.CodeGenerator.Main (System.String[] args) [0x0000c] in <fc31e3500e9a44b181504040e11d2f7d>:0  

We cannot reproduce how to do this, so we're currently assuming this is some sort of bytecode manipulation. As such, we are going to have generator ignore types with an empty name and types that end in a period, which would indicate a nested type with an empty name.