[erp5_web_renderjs_ui] fix changing relation input state with empty value_text

Changing the state of a relation_input gadget with value_text = ""
now updates the field.

bt5/erp5_web_renderjs_ui/PathTemplateItem/web_page_module/rjs_gadget_erp5_relation_input_js.js

@@ -213,7 +213,7 @@
 
       gadget.element.querySelector(".search_ul").innerHTML = "";
       // Display the airplane link or the search button
-      if ((gadget.state.value_relative_url) || (gadget.state.value_text)) {
+      if ((gadget.state.value_relative_url) || (gadget.state.value_text !== undefined)) {
         createEditableLink(gadget, JUMP_UNKNOWN_CLASS_STR);
       } else {
         return createEditableButton(gadget, SEARCH_CLASS_STR);
@@ -233,7 +233,7 @@
 
           // uid is known
           // User selected a document from a listbox
-          if ((gadget.state.value_uid) && (!gadget.state.value_text)) {
+          if ((gadget.state.value_uid) && (gadget.state.value_text === undefined)) {
             plane.className = SEARCHING_CLASS_STR;
             return gadget.detachChangeState(gadget.state.value_uid,
                                             gadget.state.catalog_index);