title: How to get localStream when receiving call in SIP.js (to mute microphone)
body: <p>When I want to mute microphone I use mediastream which I get from </p>
  
  <pre><code>session.sessionDescriptionHandler.on('userMedia', 
  onUserMediaObtained.bind(this))
  
  function onUserMediaObtained(stream) {
      localMediaStream = stream
  }
  </code></pre>
  
  <p>Session value is from agent.invite() method.</p>
  
  <p>But when I get incoming call, in onInvite event handler:</p>
  
  <pre><code>agent.on('invite', onInvite(dispatch, store))
  
  const onInvite = (dispatch, store) =&gt; session =&gt; {
    if (session.sessionDescriptionHandler) {}
    else { //always undefined here}
   }
  </code></pre>
  
  <p>I try again attach event in onaccepted event handler</p>
  
  <pre><code>session.on('accepted', onAccepted(dispatch))
  </code></pre>
  
  <p>There is sessionDescriptionHandler object initialized, but I think it's too late, onUserMediaObtained isn't fired.</p>