[BUGFIX] js errors

frontend/main.ts

@@ -20,6 +20,8 @@ document.addEventListener('DOMContentLoaded', function() {
 
 function selectBoatChange() {
   const boatSelect = <HTMLSelectElement>document.querySelector('#boat_id');
+
+  if(boatSelect) {
     const boatChoice = new Choices(boatSelect, {
       loadingText: 'Wird geladen...',
       noResultsText: 'Keine Ergebnisse gefunden',
@@ -50,8 +52,10 @@ function selectBoatChange() {
     } as any);
   
     choiceObjects[boatSelect.id] = boatChoice;
+  }
 
   const shipmasterSelect = <HTMLSelectElement>document.querySelector('#shipmaster');
+  if(shipmasterSelect) {
     const shipmasterChoice = new Choices(shipmasterSelect, {
       loadingText: 'Wird geladen...',
       noResultsText: 'Keine Ergebnisse gefunden',
@@ -61,6 +65,7 @@ function selectBoatChange() {
     
     choiceObjects[shipmasterSelect.id] = shipmasterChoice;
   }
+}
 
 function setMaxAmountRowers(rowers: number){
 	  let curSelection = choiceObjects['newrower'].getValue(true);