Add "open" guard for AsarUtil to fix concurrent builds

[elliottkember]

Fixes #5565 by adding an .on("open", () => {}) guard around using the file stream.

From the documentation:

// This will wait until we know the readable stream is actually valid before piping
readStream.on('open', function () {
  // This just pipes the read stream to the response object (which goes to the client)
  readStream.pipe(res);
});

The original createReadStream call, without a guard, fails on my M1 mac when building multiple architectures with larger files (>7mb). This change makes packaging totally reliable and is best practice for a readStream.

[elliottkember]

@develar this seems like a pretty simple PR, could you please merge?