fix: tool server save error handling

src/lib/components/AddToolServerModal.svelte

@@ -284,6 +284,7 @@
 				headers = JSON.stringify(_headers, null, 2);
 			} catch (error) {
 				toast.error($i18n.t('Headers must be a valid JSON object'));
+				loading = false;
 				return;
 			}
 		}