Fix HidlReturnRestriction for operator= case.

elsk@ noticed we were missing this case.

Bug: N/A
Test: added test fails w/o fix, but now succeeds
Change-Id: I2984e7b680144a7fe0d243e45be80461149176c8
diff --git a/base/include/hidl/Status.h b/base/include/hidl/Status.h
index 07d352f..74901bb 100644
--- a/base/include/hidl/Status.h
+++ b/base/include/hidl/Status.h
@@ -141,6 +141,11 @@
         Status mStatus {};
         mutable bool mCheckedStatus = false;
 
+        // called when an unchecked status is discarded
+        // makes sure this status is checked according to the preference
+        // set by setProcessHidlReturnRestriction
+        void onIgnored() const;
+
         template <typename T, typename U>
         friend Return<U> StatusOf(const Return<T> &other);
     protected: