Fix chromoting client crash.

The client plugin may crash if a signaling message is receive before the 
client started connection. It's likely to be a leftover from a previous 
session, so it's safe to ignore it.

BUG=226775


Review URL: https://chromiumcodereview.appspot.com/13594011

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@192923 0039d316-1c4b-4281-b951-d872f2087c98

remoting/client/plugin/chromoting_instance.cc

@@ -650,6 +650,9 @@ void ChromotingInstance::Disconnect() {
 }
 
 void ChromotingInstance::OnIncomingIq(const std::string& 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);
 }