Disable Email Alert if field does not exist

[anandpdoshi]

In trigger email alert, if the field specified in date_changed or value_changed does not exist anymore .i.e catch the below exception, disable the email alert and notify the user that it is disabled to prevent future errors.

Traceback (most recent call last):
  File "/home/frappe/press/benches/1505261338/env/lib/python2.7/site-packages/celery/app/trace.py", line 240, in trace_task
    R = retval = fun(*args, **kwargs)
  File "/home/frappe/press/benches/1505261338/env/lib/python2.7/site-packages/celery/app/trace.py", line 438, in __protected_call__
    return self.run(*args, **kwargs)
  File "/home/frappe/press/benches/1505261338/apps/frappe/frappe/tasks.py", line 77, in scheduler_task
    frappe.get_attr(handler)()
  File "/home/frappe/press/benches/1505261338/apps/frappe/frappe/email/doctype/email_alert/email_alert.py", line 23, in trigger_daily_alerts
    trigger_email_alerts(None, "daily")
  File "/home/frappe/press/benches/1505261338/apps/frappe/frappe/email/doctype/email_alert/email_alert.py", line 43, in trigger_email_alerts
    (nowdate(), diff_days or 0)):
  File "/home/frappe/press/benches/1505261338/apps/frappe/frappe/database.py", line 192, in sql_list
    return [r[0] for r in self.sql(query, values, debug=debug)]
  File "/home/frappe/press/benches/1505261338/apps/frappe/frappe/database.py", line 135, in sql
    self._cursor.execute(query, values)
  File "/home/frappe/press/benches/1505261338/env/lib/python2.7/site-packages/MySQLdb/cursors.py", line 205, in execute
    self.errorhandler(self, exc, value)
  File "/home/frappe/press/benches/1505261338/env/lib/python2.7/site-packages/MySQLdb/connections.py", line 36, in defaulterrorhandler
    raise errorclass, errorvalue
OperationalError: (1054, "Unknown column 'visa_exp_date' in 'where clause'")

[anandpdoshi]

• Could also add comment to the disabled Email Alert about what exactly was the error i.e. Unknown column 'visa_exp_date' in 'where clause'