refactor: improve module save functionality and nullable value handling

Updated the saveMod function to ensure the module is reloaded after a successful update, enhancing data consistency. Refined the nullableSelectValue and fromNullableSelect functions to handle empty string cases, improving input validation and user experience in module pages.

web/src/routes/modules/[moduleId]/+page.svelte

@@ -271,7 +271,8 @@
 	async function saveMod() {
 		editSaving = true;
 		try {
-			mod = await apiMutate<ModuleRow>(`/v1/modules/${moduleId}`, 'PATCH', editForm);
+			await apiMutate<ModuleRow>(`/v1/modules/${moduleId}`, 'PATCH', editForm);
+			await loadMod();
 			toast.success('Модуль обновлён');
 			editDialog = false;
 		} catch (e) {
@@ -723,11 +724,13 @@
 	}
 
 	function nullableSelectValue(value: string | null | undefined): string {
-		return value ?? NONE_OPTION;
+		if (value === null || value === undefined || value === '') return NONE_OPTION;
+		return value;
 	}
 
 	function fromNullableSelect(value: string): string | null {
-		return value === NONE_OPTION ? null : value;
+		if (value === NONE_OPTION || value === '') return null;
+		return value;
 	}
 
 	const activeTab = $derived.by(() => {