improved handling of null values when mapping entities to json

frontend/src/routes/task/Add.svelte

@@ -84,7 +84,9 @@
         });
         if (resp.ok) {
             task = await resp.json();
-            router.navigate(`/task/${task.id}/view`);
+            if (task.parent_task_id){
+                router.navigate(`/task/${task.parent_task_id}/view`);
+            } else router.navigate(`/task/${task.id}/view`);
             error = null;
         } else {
             error = await resp.text();

frontend/src/routes/task/View.svelte

@@ -175,9 +175,11 @@
             </td>
         </tr>
         <tr>
-            <th>{t('subtasks')}</th>
-            <td class="children">
+            <th>
+                {t('subtasks')}
                 <button onclick={addChild} >{t('add_subtask')}</button>
+            </th>
+            <td class="children">
                 {#if children}
                 <TaskList tasks={children} {estimated_time} />
                 {/if}