vzdump: check that notes-template is a single line

While vzdump itself wouldn't mind about unescaped newlines, the
parameter isn't supposed to contain any, and when used as part of the
job config, it has to be a single line too, so make it consistent.

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

PVE/VZDump.pm

@@ -1326,6 +1326,9 @@ sub verify_vzdump_parameters {
 
     $parse_prune_backups_maxfiles->($param, 'CLI parameters');
 
+    raise_param_exc({'notes-template' => "contains a line feed"})
+	if $param->{'notes-template'} && $param->{'notes-template'} =~ m/\n/;
+
     $param->{all} = 1 if (defined($param->{exclude}) && !$param->{pool});
 
     return if !$check_missing;