erp5_web_renderjs_ui: content-type header can be null

Like when the browser is offline.

bt5/erp5_web_renderjs_ui/PathTemplateItem/web_page_module/rjs_gadget_erp5_launcher_js.js

@@ -156,7 +156,8 @@
         }
       }
       if (error instanceof XMLHttpRequest) {
-        if (error.getResponseHeader('Content-Type').indexOf('text/') === 0) {
+        if ((error.getResponseHeader('Content-Type') || "")
+            .indexOf('text/') === 0) {
           error_response = error.response;
         }
         error = {

bt5/erp5_web_renderjs_ui/PathTemplateItem/web_page_module/rjs_gadget_erp5_launcher_js.xml

@@ -234,7 +234,7 @@
                   </item>
                   <item>
                       <key> <string>serial</string> </key>
-                      <value> <string>982.16935.24089.33911</string> </value>
+                      <value> <string>982.26879.4100.14950</string> </value>
                   </item>
                   <item>
                       <key> <string>state</string> </key>
@@ -252,7 +252,7 @@
                           </tuple>
                           <state>
                             <tuple>
-                              <float>1583166534.25</float>
+                              <float>1585300343.55</float>
                               <string>UTC</string>
                             </tuple>
                           </state>