Update thumbnail generation example to use cursors

src/cursors.ts

@@ -930,7 +930,6 @@ export abstract class SampleCursor<
 		this._lastPendingRequest = pendingRequest;
 
 		this._pumpGate.open();
-
 		deferred.execute(); // Waiting for the return would be too long
 
 		return res.set(await request.promise);
@@ -987,6 +986,7 @@ export abstract class SampleCursor<
 		}
 		this._lastPendingRequest = pendingRequest;
 
+		this._pumpGate.open();
 		lock.release(); // Waiting for the return would be too long
 
 		return res.set(await request.promise);

src/isobmff/isobmff-demuxer.ts

@@ -2368,7 +2368,10 @@ abstract class IsobmffTrackBacking implements InputTrackBacking {
 	}
 
 	async getFirstTimestamp() {
-		const firstPacket = await this.getFirstPacket({ metadataOnly: true });
+		const result = new ResultValue<EncodedPacket | null>();
+		await this.getFirstPacket(result, { metadataOnly: true });
+
+		const firstPacket = result.value;
 		return firstPacket?.timestamp ?? 0;
 	}