Allow for unknown stops in side pane

src/front/index.js

@@ -29,7 +29,9 @@ setInterval(() => {
 
         const timeToHTML = time => Math.ceil((time - Date.now()) / 1000);
 
-        const stopToHTML = stopId => network.stops[stopId].properties.name;
+        const stopToHTML = stopId => stopId in network.stops ?
+            network.stops[stopId].properties.name :
+            '<em>Arrêt inconnu</em>';
 
         const passingsToHTML = passings => passings.map(([stopId, time]) => `
             <tr>