fix: don't copy if src doesn't exist

src/upgrades/1.17.0/default_favicon.js

@@ -11,8 +11,9 @@ module.exports = {
 	method: async function () {
 		const pathToIco = path.join(nconf.get('upload_path'), 'system', 'favicon.ico');
 		const defaultIco = path.join(nconf.get('base_dir'), 'public', 'favicon.ico');
-		const exists = await file.exists(pathToIco);
+		const targetExists = await file.exists(pathToIco);
-		if (!exists) {
+		const defaultExists = await file.exists(defaultIco);
+		if (defaultExists && !targetExists) {
 			await fs.promises.copyFile(defaultIco, pathToIco);
 		}
 	},