Correct message template warning in MessageTemplates.php

[spalmstr]

Overview

Before

When a mailing template did not have a subject, CiviCRM gave this error:
Warning: Undefined array key "msg_subject" in content_6xxxx (line 308 of sites\default\files\civicrm\templates_c\xxxx.file.MessageTemplates.tpl.php).

After

No error message is displayed

Technical Details

We test if $messageTemplate->msg_subject is set around line 263 of /CRM/Admin/Page/MessageTemplates.php and if not set assign it to the empty string. Thus eliminates the warning message.

Comments

Anything else you would like the reviewer to note

[civibot]

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[demeritcowboy]

This seems ok.
I'm curious but not going to think too much about it: Subject is just a plain old text field, so saving with it blank should submit a empty string value which I would have thought would get saved as an empty string. But maybe it has to do with how the schema is defined and it ends up being null/missing, since there's that overlap between required/null.