Create answer problem.

Hi, great work with this plugin.

I'm facing into answer generation problem
...
PeerEventsInstance.SetRemoteDescription("offer", sdp);
PeerEventsInstance.CreateAnswer();
...
After CreateAnswer is called, unity shows me this error

```
PeerConnection cannot create an answer in a state other than have-remote-offer or have-local-pranswer.
UnityEngine.Debug:LogError(Object)
UnityWebrtc.WebrtcPeerEvents:OnFailure_Listener(String) (at Assets/UnityWebrtc/WebrtcPeerEvents.cs:189)
UnityEngine.Events.UnityEvent`1:Invoke(String)
UnityWebrtc.<>c__DisplayClass20_0:b__0() (at Assets/UnityWebrtc/WebrtcPeerEvents.cs:233)
UnityWebrtc.WebrtcPeerEvents:Update() (at Assets/UnityWebrtc/WebrtcPeerEvents.cs:155)

```
Surfing on web i found that a solution can be call CreateAnswer after SetRemoteDescritpion has finished completly ( setRemoteDescription.then(...) ), so i tried to call CreateAsnwer after some seconds without success.
Any idea?
Thanks

Start with the SetRemoteDescription and CreateAnswer calls in the issue, then inspect Assets/UnityWebrtc/WebrtcPeerEvents.cs around lines 155, 189, and 233. Reproduce the Unity error and trace the peer connection state before CreateAnswer; done means the reported answer-generation sequence no longer logs the invalid-state failure.

Written by the indexing model from the issue text.