[fix] If APP_BASE is empty, go to '/' instead of an empty string. (#785)

* if APP_BASE is empty, go to '/' instead of an empty string.

* run prettier

---------

Co-authored-by: Nathan Sarrazin <sarrazin.nathan@gmail.com>

src/routes/assistant/[assistantId]/+page.svelte

@@ -96,7 +96,7 @@
 					// `result` is an `ActionResult` object
 					if (result.type === "success") {
 						$settings.activeModel = data.assistant._id;
-						goto(`${base}`);
+						goto(`${base}` || "/");
 					} else {
 						await applyAction(result);
 					}