mojo: fail gracefully if ServiceRegistry can't find ServiceConnector

mojo/public/cpp/application/lib/service_registry.cc

Index: mojo/public/cpp/application/lib/service_registry.cc
diff --git a/mojo/public/cpp/application/lib/service_registry.cc b/mojo/public/cpp/application/lib/service_registry.cc
index ea22ec4e5be62684ed0366a468325bc83cc4791e..bc901dfb9245ae967276e403ca1510d558f8c3cf 100644
--- a/mojo/public/cpp/application/lib/service_registry.cc
+++ b/mojo/public/cpp/application/lib/service_registry.cc
@@ -58,7 +58,9 @@ void ServiceRegistry::ConnectToService(const mojo::String& service_url,
                                        const mojo::String& service_name,
                                        ScopedMessagePipeHandle client_handle,
                                        const mojo::String& requestor_url) {
-  if (!application_->AllowIncomingConnection(service_name, requestor_url)) {
+  if (name_to_service_connector_.find(service_name) ==
+          name_to_service_connector_.end() ||
+      !application_->AllowIncomingConnection(service_name, requestor_url)) {
     client_handle.reset();
     return;
   }