fix #4351: vzdump: send mail if job-end hook fails with mailnotification=failure

Since all tasks succeeded, previously no mail was sent in that case.

Note that the error passed to $self->sendmail() is added to the
subject of the mail if it is a single line or the beginning of the
mail otherwise. Thus changing the mail slightly compared to previously
for the case where the job-start hook fails and the case where the
job-end hook fails with mailnotification=always. But can be considered
an improvement, because the user sees the error right away.

Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>

PVE/VZDump.pm

@@ -1305,10 +1305,14 @@ sub exec_backup {
     my $totaltime = time() - $starttime;
 
     eval {
+	# otherwise $self->sendmail() will interpret it as multiple problems
+	my $chomped_err = $err;
+	chomp($chomped_err) if $chomped_err;
+
 	$self->sendmail(
 	    $tasklist,
 	    $totaltime,
-	    undef,
+	    $chomped_err,
 	    $self->{job_init_log} . $job_start_log,
 	    $job_end_log,
 	);