Add missing case analysis in handleUnimplemented().

c++/src/capnp/rpc.c++

@@ -2037,7 +2037,10 @@ private:
   void handleUnimplemented(const rpc::Message::Reader& message) {
     switch (message.which()) {
       case rpc::Message::RESOLVE: {
-        auto cap = message.getResolve().getCap();
+        auto resolve = message.getResolve();
+        switch (resolve.which()) {
+          case rpc::Resolve::CAP: {
+            auto cap = resolve.getCap();
             switch (cap.which()) {
               case rpc::CapDescriptor::NONE:
                 // Nothing to do (but this ought never to happen).
@@ -2058,6 +2061,12 @@ private:
             }
             break;
           }
+          case rpc::Resolve::EXCEPTION:
+            // Nothing to do.
+            break;
+        }
+        break;
+      }
 
       default:
         KJ_FAIL_ASSERT("Peer did not implement required RPC message type.", (uint)message.which());