[class-parse] Support class-parse --dump on java.lang.Object (#108)

Running `class-parse --dump` on `java.lang.Object` would fail:

	# on macOS, JDK 1.8 installed
	$ unzip /Library/Java/JavaVirtualMachines/jdk1.8.0_92.jdk/Contents/Home/jre/lib/rt.jar java/lang/Object.class
	$ mono class-parse.exe --dump java/lang/Object.class
	...
	class-parse: Unable to read file 'java/lang/Object.class': Object reference not set to an instance of an object

Enabling verbose output (`class-parse -v`) didn't help:

	$ mono class-parse.exe -v --dump java/lang/Object.class
	Unhandled Exception:
	System.IndexOutOfRangeException: Index was outside the bounds of the array.
	  at Mono.Options.Option.Parse[T] (System.String value, Mono.Options.OptionContext c) [0x0005e] in <4d78dd3d6bb745d7a994cb7587b83fb2>:0
	  ...

Doh!

The problem with the `IndexOutOfRangeException` is a bug in
`Mono.Options-PCL.cs`: it should be using `GenericTypeArguments[0]`,
*not* `GenericTypeParameters[0]`. Fix that.

Once that is fixed, we see that the `NullReferenceException` is coming
from accessing `ClassFile.SuperClass.Name`, because `java.lang.Object`
*has no superclass*, and thus `ClassFile.SuperClass` returns `null`.
Properly check for that.

With those changes in place, `class-parse --dump java.lang.Object`
works as intended:

	$ mono class-parse.exe --dump java/lang/Object.class
	.class version: 52.0
	...
	Methods Count: 12
	...
	 	11: finalize ()V Protected
	 		Code(10, Unknown[LineNumberTable](6))
	 		Exceptions(java/lang/Throwable)

Author: jonpryor

tools/class-parse/Mono.Options-PCL.cs

@@ -530,7 +530,7 @@ protected static T Parse<T> (string value, OptionContext c)
 			bool nullable = ti.IsValueType && ti.IsGenericType &&
 			                !ti.IsGenericTypeDefinition &&
 			                tt.GetGenericTypeDefinition () == typeof(Nullable<>);
-			Type targetType = nullable ? tt.GetTypeInfo ().GenericTypeParameters [0] : typeof(T);
+			Type targetType = nullable ? tt.GetTypeInfo ().GenericTypeArguments [0] : typeof(T);
 			//TypeConverter conv = TypeDescriptor.GetConverter (targetType);
 			T t = default (T);
 			try {

tools/class-parse/Program.cs

@@ -139,7 +139,7 @@ static void DumpClassFile (string file, TextWriter output)
 				output.WriteLine ("\t{0}: {1}", i, c.ConstantPool [i]);
 			}
 			output.WriteLine ("ThisClass: {0}", c.ThisClass.Name);
-			output.WriteLine ("SuperClass: {0}", c.SuperClass.Name);
+			output.WriteLine ("SuperClass: {0}", c.SuperClass?.Name);
 			output.WriteLine ("AccessFlags: {0}", c.AccessFlags);
 			output.WriteLine ("Attributes Count: {0}", c.Attributes.Count);
 			for (int i = 0; i < c.Attributes.Count; ++i) {