Fix chromoting client crash.

remoting/client/plugin/chromoting_instance.cc

Index: remoting/client/plugin/chromoting_instance.cc
diff --git a/remoting/client/plugin/chromoting_instance.cc b/remoting/client/plugin/chromoting_instance.cc
index 1514466c803f59e613883b6326b878a25f4daacf..f5d9bd1dff043105f0cc1c58c162ff5e6b5c676e 100644
--- a/remoting/client/plugin/chromoting_instance.cc
+++ b/remoting/client/plugin/chromoting_instance.cc
@@ -616,7 +616,10 @@ void ChromotingInstance::Disconnect() {
 }
 
 void ChromotingInstance::OnIncomingIq(const std::string& iq) {
-  xmpp_proxy_->OnIq(iq);
+  // Just ignore the message if it's received before Connect() is called. It's
+  // likely to be a leftover from a previous session, so it's safe to ignore it.
+  if (xmpp_proxy_)
+    xmpp_proxy_->OnIq(iq);
 }
 
 void ChromotingInstance::ReleaseAllKeys() {