plugin XEP-0050: fix handling of form submitted in the first request:

form submitted on first request (without retrieval first) was broken, this patch fixes it.

libervia/backend/plugins/plugin_xep_0050.py

@@ -580,16 +580,23 @@ class AdHocCommandHandler(XMPPHandler):
                 )
                 await self._send_error(Error.BAD_ACTION, session_id, iq_elt)
                 return
-            # This is the first request, if a initial form is specified, we return it
-            # directly.
+            # This is the first request, if an initial form is specified, we return it
+            # directly, unless the client already submitted it: we then record it as
+            # forms[0] and process them directly
             if self.command.form is not None:
-                await self._send_answer(
-                    AdHocCallbackData(form=self.command.form, status=Status.EXECUTING),
-                    session_id,
-                    session_data_private,
-                    iq_elt,
-                )
-                return
+                if next(command_elt.elements(data_form.NS_X_DATA, "x"), None):
+                    forms[0] = self.command.form
+                    page_idx = session_data_private["page_idx"] = 1
+                else:
+                    await self._send_answer(
+                        AdHocCallbackData(
+                            form=self.command.form, status=Status.EXECUTING
+                        ),
+                        session_id,
+                        session_data_private,
+                        iq_elt,
+                    )
+                    return
 
         if action == Action.CANCEL:
             ret_data = AdHocCallbackData(form=None, status=Status.CANCELED)