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/entrypoints/entrypoint_utils.cc b/runtime/entrypoints/entrypoint_utils.cc
index fb8139b..6301362 100644
--- a/runtime/entrypoints/entrypoint_utils.cc
+++ b/runtime/entrypoints/entrypoint_utils.cc
@@ -39,7 +39,7 @@
 namespace art {
 
 void CheckReferenceResult(Handle<mirror::Object> o, Thread* self) {
-  if (o.Get() == nullptr) {
+  if (o == nullptr) {
     return;
   }
   // Make sure that the result is an instance of the type this method was expected to return.