Avoid creating offer before last negotiation ended (#436)

Co-authored-by: jianjunz <jianjun.zhu@intel.com>

Author: starwarfan

src/sdk/conference/channel.js

@@ -204,6 +204,10 @@ export class ConferencePeerConnectionChannel extends EventDispatcher {
       mediaOptions.video = false;
     }
 
+    const internalId = this._createInternalId();
+    // Waiting for previous SDP negotiation if needed
+    await this._chainSdpPromise(internalId);
+
     const offerOptions = {};
     const transceivers = [];
     if (typeof this._pc.addTransceiver === 'function') {
@@ -278,11 +282,7 @@ export class ConferencePeerConnectionChannel extends EventDispatcher {
       offerOptions.offerToReceiveAudio = false;
       offerOptions.offerToReceiveVideo = false;
     }
-
-    const internalId = this._createInternalId();
     this._publishTransceivers.set(internalId, {transceivers});
-    // Waiting for previous SDP negotiation if needed
-    await this._chainSdpPromise(internalId);
 
     let localDesc;
     this._pc.createOffer(offerOptions).then((desc) => {
@@ -441,6 +441,10 @@ export class ConferencePeerConnectionChannel extends EventDispatcher {
       mediaOptions.video = false;
     }
 
+    const internalId = this._createInternalId();
+    // Waiting for previous SDP negotiation if needed
+    await this._chainSdpPromise(internalId);
+
     const offerOptions = {};
     const transceivers = [];
     this._createPeerConnection();
@@ -471,14 +475,9 @@ export class ConferencePeerConnectionChannel extends EventDispatcher {
       offerOptions.offerToReceiveAudio = !!options.audio;
       offerOptions.offerToReceiveVideo = !!options.video;
     }
-
-    const internalId = this._createInternalId();
     this._subscribeTransceivers.set(internalId, {transceivers});
     this._subscribedStreams.set(internalId, stream);
 
-    // Waiting for previous SDP negotiation if needed
-    await this._chainSdpPromise(internalId);
-
     let localDesc;
     this._pc.createOffer(offerOptions).then((desc) => {
       localDesc = desc;