Fix a bug in Dbg::GetClassDescriptor.

The callers were incorrectly assuming we always returned a descriptor, which
isn't true when handed bad input.

Change-Id: I5509d18d8c234d97fa5ec2e0a01d4cdb44acfc55
diff --git a/src/debugger.h b/src/debugger.h
index 5089995..625f941 100644
--- a/src/debugger.h
+++ b/src/debugger.h
@@ -131,7 +131,7 @@
   /*
    * Class, Object, Array
    */
-  static std::string GetClassDescriptor(JDWP::RefTypeId id);
+  static std::string GetClassName(JDWP::RefTypeId id);
   static bool GetClassObject(JDWP::RefTypeId id, JDWP::ObjectId& classObjectId);
   static JDWP::JdwpError GetSuperclass(JDWP::RefTypeId id, JDWP::RefTypeId& superclassId);
   static JDWP::ObjectId GetClassLoader(JDWP::RefTypeId id);