[TRI-3068] Strip out more unicode null characters

[matt-aitken]

It seems like some TaskEvents aren't being checked for unicode null characters:

400 "\nInvalid prisma.taskEvent.create() invocation:\n\n\nError occurred during query execution:\nConnectorError(ConnectorError { user_facing_error: None, kind: QueryError(PostgresError { code: "22P05", message: "unsupported Unicode escape sequence", severity: "ERROR", detail: Some("\\u0000 cannot be converted to text."), column: None, hint: None }), transient: false })"

Probably in the task output is my guess.

_TRI-3068