Fix wrong handling of non-text messages

This happened only when there were commands registered, and a non-text
message was sent to the bot. Regression introduced in 350a78a.

Author: Pietro Albini

botogram/hooks.py

@@ -39,7 +39,7 @@ def _after_init(self, args):
 
     def call(self, bot, update):
         """Call the hook"""
-        if self._only_texts and update.message is None:
+        if self._only_texts and update.message.text is None:
             return
         return self._call(bot, update)