THRIFT-2092 TNonblocking server should release handler as soon as connection closes

Patch: Konrad Grochowski
diff --git a/lib/cpp/src/thrift/server/TNonblockingServer.cpp b/lib/cpp/src/thrift/server/TNonblockingServer.cpp
index 1552e89..43cdc50 100644
--- a/lib/cpp/src/thrift/server/TNonblockingServer.cpp
+++ b/lib/cpp/src/thrift/server/TNonblockingServer.cpp
@@ -840,6 +840,9 @@
   factoryInputTransport_->close();
   factoryOutputTransport_->close();
 
+  // release processor and handler
+  processor_.reset();
+
   // Give this object back to the server that owns it
   server_->returnConnection(this);
 }