Fix googleapis#183 When trying to send a message that is a saved draf…

…t and has uncommitted changes, call save draft before sending.

O365/message.py

@@ -602,7 +602,11 @@ def send(self, save_to_sent_folder=True):
         if self.__is_draft and self.object_id:
             url = self.build_url(
                 self._endpoints.get('send_draft').format(id=self.object_id))
+            if self._track_changes:
+                # there are pending changes to be committed
+                self.save_draft()
             data = None
+
         else:
             url = self.build_url(self._endpoints.get('send_mail'))
             data = {self._cc('message'): self.to_api_data()}