Merge pull request #2070 from cloudflare/kenton/rpc-fix-output-gate

Fix UAF in recent RPC output gate change.

src/workerd/api/worker-rpc.c++

@@ -1059,7 +1059,7 @@ public:
         })));
 
         if (ctx.hasOutputGate()) {
-          return result.then([this]() {
+          return result.then([weakIoContext = weakIoContext->addRef()]() mutable {
             return KJ_REQUIRE_NONNULL(weakIoContext->tryGet()).waitForOutputLocks();
           });
         } else {