Added checks to make sure the specified track exists

Added precondition checks to validate input files and paths to return more informative error messages as per #2

node_modules/is-wsl/index.js

@@ -0,0 +1,25 @@
+'use strict';
+const os = require('os');
+const fs = require('fs');
+
+const isWsl = () => {
+	if (process.platform !== 'linux') {
+		return false;
+	}
+
+	if (os.release().includes('Microsoft')) {
+		return true;
+	}
+
+	try {
+		return fs.readFileSync('/proc/version', 'utf8').includes('Microsoft');
+	} catch (err) {
+		return false;
+	}
+};
+
+if (process.env.__IS_WSL_TEST__) {
+	module.exports = isWsl;
+} else {
+	module.exports = isWsl();
+}