'Genericise' errors ready for +error.svelte upgrade to handle known errors

src/routes/trains/+page.ts

@@ -1,4 +1,4 @@
-import { OwlClient, ApiError, ValidationError } from '$lib/owlClient';
+import { OwlClient, ApiError, ValidationError, ThrowApiError } from '$lib/owlClient';
 import type { ApiTrainsTrainByHeadcode } from '@owlboard/owlboard-ts';
 import type { PageLoad } from './$types';
 import { error } from '@sveltejs/kit';
@@ -10,31 +10,21 @@ export const load: PageLoad = async ({ fetch, url }) => {
 
 	const date: string | Date = dateParam === '' || dateParam === null ? new Date() : dateParam;
 
-	if (!headcode) {
-		throw error(400, {
-			message: 'Headcode not provided',
-			owlCode: 'INVALID_DATA'
-		});
-	}
+	// Validation removed, handled by the API Client Lib
 
 	// Declared outside of the try so that it can be used in both the try and catch blocks
 	let results: ApiTrainsTrainByHeadcode.TrainByHeadcodeResponse[];
 
 	try {
-		const response = await OwlClient.trains.getByHeadcode(headcode, date, toc, fetch);
+		const response = await OwlClient.trains.getByHeadcode(headcode || '', date, toc, fetch);
 
+		let title = !!headcode ? headcode.toUpperCase() : 'Error';
 		results = response.data;
 		return {
-			title: headcode.toUpperCase(),
+			title: title,
 			results: results
 		};
 	} catch (e: unknown) {
-		if (e instanceof TypeError && e.message === 'Failed to fetch') {
-			error(503, {
-				message: 'Cannot connect to the OwlBoard server',
-				owlCode: 'NETWORK_DISCONNECTED'
-			});
-		}
-		throw e;
+		ThrowApiError(e);
 	}
 };