Fix a case where "password_by_talk" was not a boolean (e.g. null or "0") and...

Fix a case where "password_by_talk" was not a boolean (e.g. null or "0") and actively cast it to a boolean

This was the error message that we have seen:

```
Argument 1 passed to OC\\Share20\\Share::setSendPasswordByTalk() must be of the type boolean, null given, called in apps/sharebymail/lib/ShareByMailProvider.php on line 981
```

Signed-off-by: Morris Jobke <hey@morrisjobke.de>