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/test_main.cpp b/test_main.cpp
index fc71231..e4cdd29 100644
--- a/test_main.cpp
+++ b/test_main.cpp
@@ -546,6 +546,36 @@
             "");
 }
 
+TEST_F(LibHidlTest, DetectUncheckedReturn) {
+    using ::android::hardware::HidlReturnRestriction;
+    using ::android::hardware::Return;
+    using ::android::hardware::setProcessHidlReturnRestriction;
+    using ::android::hardware::Status;
+
+    setProcessHidlReturnRestriction(HidlReturnRestriction::FATAL_IF_UNCHECKED);
+
+    EXPECT_DEATH(
+            {
+                auto ret = Return<void>(Status::ok());
+                (void)ret;
+            },
+            "");
+    EXPECT_DEATH(
+            {
+                auto ret = Return<void>(Status::ok());
+                ret = Return<void>(Status::ok());
+                ret.isOk();
+            },
+            "");
+
+    auto ret = Return<void>(Status::ok());
+    (void)ret.isOk();
+    ret = Return<void>(Status::ok());
+    (void)ret.isOk();
+
+    setProcessHidlReturnRestriction(HidlReturnRestriction::NONE);
+}
+
 std::string toString(const ::android::hardware::Status &s) {
     using ::android::hardware::operator<<;
     std::ostringstream oss;