don't leak timeline when an error is thrown while opening it

or you are just stuck with "not dealing with race" errors until refresh

src/matrix/room/BaseRoom.js

@@ -404,10 +404,16 @@ export class BaseRoom extends EventEmitter {
                 clock: this._platform.clock,
                 logger: this._platform.logger,
             });
+            try {
                 if (this._roomEncryption) {
                     this._timeline.enableEncryption(this._decryptEntries.bind(this, DecryptionSource.Timeline));
                 }
                 await this._timeline.load(this._user, this.membership, log);
+            } catch (err) {
+                // this also clears this._timeline in the closeCallback
+                this._timeline.dispose();
+                throw err;
+            }
             return this._timeline;
         });
     }