accounting_l10n_fr: make `at_date` required in FEC dialog

In the report code, this at_date is used and report generation would
fail if user does not select an `at_date`.

bt5/erp5_accounting_l10n_fr/SkinTemplateItem/portal_skins/erp5_accounting_l10n_fr/AccountingTransactionModule_viewFrenchAccountingTransactionFileDialog/your_at_date.xml

@@ -6,6 +6,14 @@
     </pickle>
     <pickle>
       <dictionary>
+        <item>
+            <key> <string>delegated_list</string> </key>
+            <value>
+              <list>
+                <string>required</string>
+              </list>
+            </value>
+        </item>
         <item>
             <key> <string>id</string> </key>
             <value> <string>your_at_date</string> </value>
@@ -71,6 +79,10 @@
                     <key> <string>form_id</string> </key>
                     <value> <string>Base_viewDialogFieldLibrary</string> </value>
                 </item>
+                <item>
+                    <key> <string>required</string> </key>
+                    <value> <int>1</int> </value>
+                </item>
                 <item>
                     <key> <string>target</string> </key>
                     <value> <string>Click to edit the target</string> </value>