Ignore BOM in locale files

Ignore BOM at the start of Factorio locale files as this is a thing
Factorio also does.

Fixes #507

packages/lib/src/ini.ts

@@ -11,6 +11,11 @@
  * @returns sections parsed from the ini file.
  */
 export function parse(input: string) {
+	// Ignore BOM at the start of the file
+	if (input[0] === "\uFEFF") {
+		input = input.slice(1);
+	}
+
 	const sections: Record<string, string | Record<string, string>> = {};
 	let currentSection: Record<string, string> = sections as Record<string, string>;
 	const lines = input.split(/\r\n|\n/);

test/file/bom.cfg

@@ -0,0 +1,2 @@
+[spam]
+foo=bar

test/lib/ini.js

@@ -1,5 +1,6 @@
 "use strict";
 const assert = require("assert").strict;
+const fs = require("fs-extra");
 const lib = require("@clusterio/lib");
 
 describe("lib/ini", function() {
@@ -58,6 +59,12 @@ describe("lib/ini", function() {
 				new Error("Duplicated key key on line 2")
 			);
 		});
+		it("should parse a file with BOM", async function() {
+			assert.deepEqual(
+				lib.parse(await fs.readFile("test/file/bom.cfg", "utf8")),
+				{ spam: { foo: "bar" }},
+			);
+		});
 	});
 	describe("stringify()", function() {
 		it("should serialize to reference output", function() {