Don't crash if STUN error message is missing ERROR-CODE attribute.

webrtc/p2p/base/relayport.cc

Index: webrtc/p2p/base/relayport.cc
diff --git a/webrtc/p2p/base/relayport.cc b/webrtc/p2p/base/relayport.cc
index 5eacf6d708e451f1d57452a8a0b4956a1639bc3d..e353511f8047c6ef92acce6d9f488e68c6a1b4ac 100644
--- a/webrtc/p2p/base/relayport.cc
+++ b/webrtc/p2p/base/relayport.cc
@@ -824,7 +824,7 @@ void AllocateRequest::OnResponse(StunMessage* response) {
 void AllocateRequest::OnErrorResponse(StunMessage* response) {
   const StunErrorCodeAttribute* attr = response->GetErrorCode();
   if (!attr) {
-    LOG(INFO) << "Bad allocate response error code";
+    LOG(LS_ERROR) << "Missing allocate response error code.";
   } else {
     LOG(INFO) << "Allocate error response:"
               << " code=" << attr->code()