Sorting by 'From' creates errro

[rbonatuvic]

When sorting by 'From' field, a 'Data error.' is thrown.
This text is placed between the column headers and the message headers table.
The messages are not sorted.

[rbonatuvic]

The firstname and lastname fields need to be added to the select statement.
Line 210 of block_jmail_mailbox.class.php is:

$select = "SELECT DISTINCT(m.id), m.courseid, m.subject, m.timesent, m.timecreated, m.sender, m.approved";

but should be:

$select = "SELECT DISTINCT(m.id), m.courseid, m.subject, m.timesent, m.timecreated, m.sender, m.approved, u.firstname, u.lastname";