Don't throw an exception when budget response has no errors attribute

src/routes/+page.svelte

@@ -1348,7 +1348,7 @@
           {#if displayMode.budget}
             {#if displayMode.parametersVariableName !== undefined}
               <div class="mb-6 flex flex-col px-2 lg:px-5 w-screen md:w-full">
-                {#if $budgetSimulation === undefined || $budgetSimulation.errors.length > 0}
+                {#if $budgetSimulation === undefined || ($budgetSimulation.errors != null && $budgetSimulation.errors.length > 0)}
                   {#if displayMode.parametersVariableName !== undefined}
                     <div class="z-10 bg-le-jaune bg-opacity-20">
                       <Spinner />