health: Check return value of LinkedCallback::Make.

If LinkedCallback::Make returns nullptr, do not put it
in Health::callback_. Otherwise, OnHealthInfoChanged
crashes later because the linked callback objects are
not null checked before accessing.

Test: android.hardware.health-service.aidl_fuzzer (with
  a special corpus)
Fixes: 289599278
Change-Id: I8bad41dbcfbefeb54744059baffd4eef1ae7ec42
diff --git a/health/aidl/default/LinkedCallback.h b/health/aidl/default/LinkedCallback.h
index 82490a7..da494c9 100644
--- a/health/aidl/default/LinkedCallback.h
+++ b/health/aidl/default/LinkedCallback.h
@@ -20,6 +20,7 @@
 
 #include <aidl/android/hardware/health/IHealthInfoCallback.h>
 #include <android-base/macros.h>
+#include <android-base/result.h>
 #include <android/binder_auto_utils.h>
 
 #include <health-impl/Health.h>
@@ -34,8 +35,8 @@
     // service->death_reciepient() should be from CreateDeathRecipient().
     // Not using a strong reference to |service| to avoid circular reference. The lifetime
     // of |service| must be longer than this LinkedCallback object.
-    static std::unique_ptr<LinkedCallback> Make(std::shared_ptr<Health> service,
-                                                std::shared_ptr<IHealthInfoCallback> callback);
+    static ::android::base::Result<std::unique_ptr<LinkedCallback>> Make(
+            std::shared_ptr<Health> service, std::shared_ptr<IHealthInfoCallback> callback);
 
     // Automatically unlinkToDeath upon destruction. So, it is always safe to reinterpret_cast
     // the cookie back to the LinkedCallback object.