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/method_handles.cc b/runtime/method_handles.cc
index 99886e5..834abbb 100644
--- a/runtime/method_handles.cc
+++ b/runtime/method_handles.cc
@@ -220,7 +220,7 @@
     StackHandleScope<2> hs(Thread::Current());
     Handle<mirror::Class> h_to(hs.NewHandle(to));
     Handle<mirror::Object> h_obj(hs.NewHandle(src_value.GetL()));
-    if (h_obj.Get() != nullptr && !to->IsAssignableFrom(h_obj->GetClass())) {
+    if (h_obj != nullptr && !to->IsAssignableFrom(h_obj->GetClass())) {
       ThrowClassCastException(h_to.Get(), h_obj->GetClass());
       return false;
     }
@@ -599,7 +599,7 @@
 
     // Something went wrong while creating the emulated stack frame, we should
     // throw the pending exception.
-    if (sf.Get() == nullptr) {
+    if (sf == nullptr) {
       DCHECK(self->IsExceptionPending());
       return false;
     }