[maildropl] Adding to the KEYWORDS variable one at a time

[email b. <ema...@ya...>]

If I have multiple rules in a maildrop filter file that add various keywords to 
the KEYWORDS variable, how do I make sure that each rule doesn't overwrite the 
keywords added by previous rules?  And how do I make sure that if KEYWORDS is 
empty (not used previous to a given rule) I add to it without causing any 
error?  Is it always guaranteed to be available as an empty string?

What I'm using right now is this:

if (/^Subject: .*important/:h)
{
  KEYWORDS=$KEYWORDS',$label1'
}

if (/^Subject: .*work/:h)
{
  KEYWORDS=$KEYWORDS',$label2'
}

But technically, this should mean KEYWORDS has a comma on the beginning that's 
not needed:

,$label1,$label2

Is that OK? Should I do something like this?

if (/^Subject: .*important/:h)
{
  if ("$KEYWORDS" ne "") 
  {
    KEYWORDS=$KEYWORDS',' 
  }
  KEYWORDS=$KEYWORDS'$label1'
}

if (/^Subject: .*work/:h)
{
  if ("$KEYWORDS" ne "") 
  {
    KEYWORDS=$KEYWORDS',' 
  }
  KEYWORDS=$KEYWORDS'$label2'
}