fix: 修正驗證碼驗證被略過錯誤

尚未發送驗證碼及不輸入驗證碼皆為空字串，新增產生的驗證碼不得為空字串處理

lib/RegisterPage.dart

@@ -150,7 +150,14 @@ class _RegisterPageState extends State<RegisterPage> {
       return false;
     }
 
-    if (code != _generatedCode) {
+    if (_generatedCode == ''){
+      ScaffoldMessenger.of(context).showSnackBar(
+        SnackBar(content: Text('請先發送驗證碼')),
+      );
+      return false;
+    }
+
+    if (code == '' || code != _generatedCode) {
       ScaffoldMessenger.of(context).showSnackBar(
         SnackBar(content: Text('驗證碼錯誤')),
       );
@@ -262,6 +269,7 @@ class _RegisterPageState extends State<RegisterPage> {
                     decoration: InputDecoration(
                       border: OutlineInputBorder(),
                       prefixIcon: Icon(Icons.person_outlined),
+                      // TODO: user name in database setting as primary is not suitable change to username would better
                       labelText: '用戶姓名',
                     ),
                   ),