message: Fix integer conversion warning
diff: @@ -156,7 +156,7 @@ public:
  // in each ObserverState with information about what changes were made.
  struct ObserverState {
  // Table and row which is observed
  - int64_t table_key;
  + uint32_t table_key;
  int64_t obj_key;
  // Opaque userdata for the delegate's use
  