build/azure-pipelines/common/createAsset.ts/doesAssetExist
async function doesAssetExist(blobService: azure.BlobService, quality: string, blobName: string): Promise<boolean | undefined> {
	const existsResult = await new Promise<azure.BlobService.BlobResult>((c, e) => blobService.doesBlobExist(quality, blobName, (err, r) => err ? e(err) : c(r)));
	return existsResult.exists;
}