Make sure to close publisher properly when GR is requested

Summary: I missed this when implementing patch publisher. When we send a request for gr, we queue an empty patch chunk and let this check break out of the publish loop. Right now we end up waiting for this for ever and crash on warmboot exit

Differential Revision:
D61443485

Privacy Context Container: L1125642

fbshipit-source-id: 2297df95d13a2784cc42be2f54a0fc67a6917869

fboss/fsdb/client/FsdbPatchPublisher.cpp

@@ -43,6 +43,12 @@ folly::coro::Task<void> FsdbPatchPublisher::serveStream(StreamT&& stream) {
             XLOG(DBG2) << " Detected cancellation";
             break;
           }
+          if (isGracefulServiceLoopCompletionRequested()) {
+            XLOG(ERR) << "Detected GR cancellation";
+            throw FsdbClientGRDisconnectException(
+                "DeltaPublisher disconnectReason: GR");
+            break;
+          }
           PublisherMessage message;
           message.set_patch(std::move(*patch));
           co_yield std::move(message);