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/mirror/emulated_stack_frame.cc b/runtime/mirror/emulated_stack_frame.cc
index 978cc32..be0eac0 100644
--- a/runtime/mirror/emulated_stack_frame.cc
+++ b/runtime/mirror/emulated_stack_frame.cc
@@ -173,13 +173,13 @@
 
   Handle<mirror::ObjectArray<mirror::Object>> references(hs.NewHandle(
       mirror::ObjectArray<mirror::Object>::Alloc(self, array_class, refs_size)));
-  if (references.Get() == nullptr) {
+  if (references == nullptr) {
     DCHECK(self->IsExceptionPending());
     return nullptr;
   }
 
   Handle<ByteArray> stack_frame(hs.NewHandle(ByteArray::Alloc(self, frame_size)));
-  if (stack_frame.Get() == nullptr) {
+  if (stack_frame == nullptr) {
     DCHECK(self->IsExceptionPending());
     return nullptr;
   }