ART: Add operator == and != with nullptr to Handle

Get it in line with ObjPtr and prettify our code.

Test: m
Change-Id: I1322e2a9bc7a85d7f2441034a19bf4d807b81a0e
diff --git a/runtime/native/java_lang_invoke_MethodHandleImpl.cc b/runtime/native/java_lang_invoke_MethodHandleImpl.cc
index 72a37f8..9113841 100644
--- a/runtime/native/java_lang_invoke_MethodHandleImpl.cc
+++ b/runtime/native/java_lang_invoke_MethodHandleImpl.cc
@@ -57,7 +57,7 @@
     }
   }
 
-  if (UNLIKELY(h_object.Get() == nullptr)) {
+  if (UNLIKELY(h_object == nullptr)) {
     soa.Self()->AssertPendingOOMException();
     return nullptr;
   }