chat: do not send empty text to assitant

MAVProxy/modules/mavproxy_chat/chat_window.py

@@ -135,7 +135,7 @@ def record_button_click_execute(self, event):
 
             # convert audio to text and place in input box
             text = self.chat_voice_to_text.convert_audio_to_text(rec_filename)
-            if text is None:
+            if text is None or text == "":
                 self.set_status_text("audio to text conversion failed")
                 return
             wx.CallAfter(self.text_input.SetValue, text)
@@ -149,6 +149,9 @@ def send_button_click(self, event):
 
     # handle text input
     def text_input_change(self, event):
+        # protect against sending empty text
+        if self.text_input.GetValue() == "":
+            return
         # send text to assistant in a separate thread
         th = Thread(target=self.send_text_to_assistant)
         th.start()