erp5_web_renderjs_ui: display error messages in hidden fields

As it is a common pattern to set validators on hidden fields
to display custom errors to users.

bt5/erp5_web_renderjs_ui/PathTemplateItem/web_page_module/rjs_gadget_erp5_label_field_js.js

@@ -107,7 +107,7 @@
       var gadget = this,
         span;
 
-      if (gadget.state.hidden) {
+      if (gadget.state.hidden && !modification_dict.error_text) {
         this.element.hidden = true;
       } else {
         this.element.hidden = false;

bt5/erp5_web_renderjs_ui/PathTemplateItem/web_page_module/rjs_gadget_erp5_label_field_js.xml

@@ -230,7 +230,7 @@
             </item>
             <item>
                 <key> <string>serial</string> </key>
-                <value> <string>964.59013.39016.42820</string> </value>
+                <value> <string>966.58912.4243.58521</string> </value>
             </item>
             <item>
                 <key> <string>state</string> </key>
@@ -248,7 +248,7 @@
                     </tuple>
                     <state>
                       <tuple>
-                        <float>1516293734.37</float>
+                        <float>1523892720.71</float>
                         <string>UTC</string>
                       </tuple>
                     </state>

bt5/erp5_web_renderjs_ui_test/PathTemplateItem/portal_tests/renderjs_ui_notification_zuite/testHiddenFieldError.zpt

@@ -48,6 +48,8 @@ Check that user gets notified if there is an error on a hidden field.
                                                            'text': 'Input data has errors.'}">
   <tal:block metal:use-macro="here/Zuite_CommonTemplateForRenderjsUi/macros/wait_for_notification" />
 </tal:block>
+<tr><td>verifyVisible</td>
+    <td>//div[@data-gadget-scope='field_my_quantity']//span[text()="Quantity can't be negative."]</td><td></td></tr>
 
 </tbody>
 </table>