Fix lack of media when a user reconnects (#3318)

* Fix lack of media when a user reconnects

This fixes broken media when someone reconnects to the call after
a forced disconnect (when their old call gets replaced immediately
by a new call). We listen for changes in the call feeds and the tearing
down of the feeds for the old call caused us to remove the feed for
the new call.

Also adds the call to the calls map before it'as initialised, such that
it's the active call for the user/device when the feedsChanged event arrives,
otherwise we'll ignore the event.

* Fix tests

spec/unit/webrtc/groupCall.spec.ts

@@ -388,6 +388,10 @@ describe("Group Call", function () {
                 call = new MockMatrixCall(room.roomId, groupCall.groupCallId);
 
                 await groupCall.create();
+
+                const deviceCallMap = new Map<string, MatrixCall>();
+                deviceCallMap.set(FAKE_DEVICE_ID_1, call.typed());
+                (groupCall as any).calls.set(FAKE_USER_ID_1, deviceCallMap);
             });
 
             it("ignores changes, if we can't get user id of opponent", async () => {

src/webrtc/groupCall.ts

@@ -881,6 +881,11 @@ export class GroupCall extends TypedEventEmitter<
         );
 
         if (prevCall) prevCall.hangup(CallErrorCode.Replaced, false);
+        // We must do this before we start initialising / answering the call as we
+        // need to know it is the active call for this user+deviceId and to not ignore
+        // events from it.
+        deviceMap.set(newCall.getOpponentDeviceId()!, newCall);
+        this.calls.set(opponentUserId, deviceMap);
 
         this.initCall(newCall);
 
@@ -895,8 +900,6 @@ export class GroupCall extends TypedEventEmitter<
         }
         newCall.answerWithCallFeeds(feeds);
 
-        deviceMap.set(newCall.getOpponentDeviceId()!, newCall);
-        this.calls.set(opponentUserId, deviceMap);
         this.emit(GroupCallEvent.CallsChanged, this.calls);
     };
 
@@ -1138,6 +1141,14 @@ export class GroupCall extends TypedEventEmitter<
         const remoteUsermediaFeed = call.remoteUsermediaFeed;
         const remoteFeedChanged = remoteUsermediaFeed !== currentUserMediaFeed;
 
+        const deviceMap = this.calls.get(opponentMemberId);
+        const currentCallForUserDevice = deviceMap?.get(opponentDeviceId);
+        if (currentCallForUserDevice?.callId !== call.callId) {
+            // the call in question is not the current call for this user/deviceId
+            // so ignore feed events from it otherwise we'll remove our real feeds
+            return;
+        }
+
         if (remoteFeedChanged) {
             if (!currentUserMediaFeed && remoteUsermediaFeed) {
                 this.addUserMediaFeed(remoteUsermediaFeed);