fix: ignore engine closed events for data track packets which are in flight / un delivered on engine close

I have noticed in running the data track end to end test, that "engine
closed" gets thrown fairly often.

I think the move away from the while/sleep loop in
waitForBufferStatusLow (which wasn't in my data track subscription
updates PR) has newly resulted in more waitForBufferStatusLow s being in
flight at once so there's a much higher likelihood that the data channel
won't be drained upon engine close.

To fix this, I've added a param to waitForBufferStatusLow to allow
ignoring engine closed events. Not sure if this is the best thing to do
but it fixes the tests, and I think matches the ethos of "send packets
as fast as possible" / doesn't introduce any sort of explicit locking.

Author: 1egoman

src/room/RTCEngine.ts

@@ -1519,7 +1519,7 @@ export default class RTCEngine extends (EventEmitter as new () => TypedEventEmit
         // buffer status to not be low before continuing.
         switch (bufferStatusLowBehavior) {
           case 'wait':
-            await this.waitForBufferStatusLow(kind);
+            await this.waitForBufferStatusLow(kind, 'ignore');
             break;
           case 'drop':
             // this.log.warn(`dropping lossy data channel message`, this.logContext);
@@ -1580,9 +1580,12 @@ export default class RTCEngine extends (EventEmitter as new () => TypedEventEmit
     }
   };
 
-  async waitForBufferStatusLow(kind: DataChannelKind) {
+  async waitForBufferStatusLow(
+    kind: DataChannelKind,
+    engineCloseBehavior: 'throw' | 'ignore' = 'throw',
+  ) {
     return new TypedPromise<void, UnexpectedConnectionState>(async (resolve, reject) => {
-      if (this.isClosed) {
+      if (this.isClosed && engineCloseBehavior === 'throw') {
         reject(new UnexpectedConnectionState('engine closed'));
       }
       if (this.isBufferStatusLow(kind)) {
@@ -1593,7 +1596,9 @@ export default class RTCEngine extends (EventEmitter as new () => TypedEventEmit
           reject(new UnexpectedConnectionState(`DataChannel not found, kind: ${kind}`));
           return;
         }
-        this.bufferStatusLowClosingFuture.promise.catch((e) => reject(e));
+        if (engineCloseBehavior === 'throw') {
+          this.bufferStatusLowClosingFuture.promise.catch((e) => reject(e));
+        }
         dc.addEventListener('bufferedamountlow', () => resolve(), {
           once: true,
         });