mxproxmox: Remove trailing white space from backup-list lines

Remove trailing whitespace from lines read from backup-list.

If we keep trailing whitespace, the following split will keep the
whitespace in $opt_limit. This is later checked with `if
defined($limit)` , which is true. Still, the empty string will evaluate
numerically to zero (with a warning). A limit zero is not what we want
here.

From `perldoc -f split`:

    When assigning to a list, if LIMIT is omitted, or zero, Perl supplies a
    LIMIT one larger than the number of variables in the list, to avoid
    unnecessary work

This has this surprising effect:

      DB<1> x split " ","a   "
    0  'a'
      DB<2> @a = split " ","a   "
      DB<3> x @s
      empty array
      DB<4> x @a
    0  'a'
      DB<5> ($a, $b) = split " ","a   "
      DB<6> x ($a, $b)
    0  'a'
    1  ''
      DB<7>

mxproxmox/mxproxmox

@@ -199,7 +199,7 @@ sub read_backup_list {
     open my $in, '<', '/etc/mxproxmox/backup-list.dat' or die "/etc/mxproxmox/backup-list.dat: $!\n";
     while (<$in>) {
         chomp;
-        s/#.*//;
+        s/\s*#.*//;
         /\S/ or next;
         my ($project, $opt_limit) = split " ";
         $INCLUDE{$project} = $opt_limit;