Fix Can't create theme when uploading a file

When trying to create a theme, you can upload
files. After the upload completes, you should be
able to proceed to the next step. However, the
"Next" button remained disabled, making it
impossible to proceed.
(Well, not actually impossible, going a step back
and then forward again would fix the issue, but w/e).

This fixes that, but crudely. We may want to rewrite
the theme dialog because uploading each file individually
and forcing the user to wait on that seems pretty
bad UX to me.

src/components/shared/wizard/FileUpload.tsx

@@ -1,5 +1,5 @@
 import { useTranslation } from "react-i18next";
-import React, { useRef, useState } from "react";
+import React, { useEffect, useRef, useState } from "react";
 import axios from "axios";
 import { NOTIFICATION_CONTEXT } from "../../../configs/modalConfig";
 import { useAppDispatch } from "../../../store";
@@ -43,6 +43,17 @@ const FileUpload = <T extends RequiredFormProps>({
 	// reference used for activating file input when button is clicked
 	const hiddenFileInput = useRef<HTMLInputElement>(null);
 
+	// Trigger formik validation
+	// Setting formik fields in a promise callback does not trigger formik
+	// validation (or at the very least, does not trigger it with the new
+	// values). Therefore, this useEffect gets manually triggered, causing an
+	// additional rerender which then triggers formik validation.
+	useEffect(() => {
+		formik.validateForm()
+	// eslint-disable-next-line react-hooks/exhaustive-deps
+	}, [formik.values.fileId, formik.values.fileName, loaded]);
+
+
 	const handleDelete = () => {
 		setFile(undefined);
 		setLoaded(0);
@@ -68,7 +79,9 @@ const FileUpload = <T extends RequiredFormProps>({
 				if (res.status === 201) {
 					// set information about file later needed for POST request and summary
 					formik.setFieldValue(fileId, res.data);
-					formik.setFieldValue(fileName, file.name);
+					formik.setFieldValue(fileName, file.name)
+					// Purely for triggering useEffect. The state change does not matter.
+					setLoaded(1337)
 				}
 			})
 			.catch((res) => {
@@ -90,6 +103,8 @@ const FileUpload = <T extends RequiredFormProps>({
 		if (e.target.files) {
 			setFile(e.target.files[0]);
 			upload(e.target.files[0]);
+			// formik.setFieldValue(fileId, e.target.files[0]);
+			// formik.setFieldValue(fileName, e.target.files[0].name);
 		}
 	};