notifications.py: don't crash if notifications recipient is invalid

On Django 3:3.2.19, if recipient is not filled or is invalid, cron
job fails with:

  Traceback (most recent call last):
    File "/usr/local/patchwork/./manage.py", line 17, in <module>
      execute_from_command_line(sys.argv)
    File "/usr/lib/python3/dist-packages/django/core/management/__init__.py", line 419, in execute_from_command_line
      utility.execute()
    File "/usr/lib/python3/dist-packages/django/core/management/__init__.py", line 413, in execute
      self.fetch_command(subcommand).run_from_argv(self.argv)
    File "/usr/lib/python3/dist-packages/django/core/management/base.py", line 354, in run_from_argv
      self.execute(*args, **cmd_options)
    File "/usr/lib/python3/dist-packages/django/core/management/base.py", line 398, in execute
      output = self.handle(*args, **options)
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    File "/usr/local/patchwork/patchwork/management/commands/cron.py", line 19, in handle
      errors = send_notifications()
               ^^^^^^^^^^^^^^^^^^^^
    File "/usr/local/patchwork/patchwork/notifications.py", line 84, in send_notifications
      message.send()
    File "/usr/lib/python3/dist-packages/django/core/mail/message.py", line 284, in send
      return self.get_connection(fail_silently).send_messages([self])
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    File "/usr/lib/python3/dist-packages/django/core/mail/backends/smtp.py", line 109, in send_messages
      sent = self._send(message)
             ^^^^^^^^^^^^^^^^^^^
    File "/usr/lib/python3/dist-packages/django/core/mail/backends/smtp.py", line 122, in _send
      recipients = [sanitize_address(addr, encoding) for addr in email_message.recipients()]
                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    File "/usr/lib/python3/dist-packages/django/core/mail/backends/smtp.py", line 122, in <listcomp>
      recipients = [sanitize_address(addr, encoding) for addr in email_message.recipients()]
                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    File "/usr/lib/python3/dist-packages/django/core/mail/message.py", line 99, in sanitize_address
      address_parts = nm + localpart + domain
                      ~~~^~~~~~~~~~~
  TypeError: can only concatenate str (not "NoneType") to str

As there's no point trying to send a notification to an invalid
e-mail, just drops it.

Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>

Author: mchehab

patchwork/notifications.py

@@ -73,6 +73,16 @@ def delete_notifications():
             'patchwork/mails/patch-change-notification.txt', context
         )
 
+        # Got one case where recipient.email == "<>". That causes Django to fail with:
+        #   File "/usr/lib/python3/dist-packages/django/core/mail/message.py", line 99, in sanitize_address
+        #    address_parts = nm + localpart + domain
+        #                    ~~~^~~~~~~~~~~
+        # TypeError: can only concatenate str (not "NoneType") to str
+        if not recipient.email or recipient.email == "<>" or recipient.email == "":
+            errors.append((recipient, "Invalid recipient"))
+            delete_notifications()
+            continue
+
         message = EmailMessage(
             subject=subject,
             body=content,