dbus: Fix a crash in UpdateEngineClientImpl::OnGetStatusError()

|error| can be NULL if the response is not received.

BUG=316986
TEST=none

Review URL: https://codereview.chromium.org/68533009

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@234474 0039d316-1c4b-4281-b951-d872f2087c98

chromeos/dbus/update_engine_client.cc

@@ -252,7 +252,8 @@ class UpdateEngineClientImpl : public UpdateEngineClient {
 
   // Called when GetStatus call failed.
   void OnGetStatusError(dbus::ErrorResponse* error) {
-    LOG(ERROR) << "GetStatus request failed with error: " << error->ToString();
+    LOG(ERROR) << "GetStatus request failed with error: "
+               << (error ? error->ToString() : "");
   }
 
   // Called when a response for SetReleaseChannel() is received.