git-grope.cgi: unbreak output with empty $url_prefix
git-grope.cgi: unbreak output with empty $url_prefix

zshexpn(1), "Empty argument removal":

> If the substitution does not appear in double quotes, any resulting
> zero-length argument, whether from a scalar or an element of an array,
> is elided from the list of arguments inserted into the command line.

for example this::

  a='foo bar'
  b=snafu
  print -f 'a="%s" b="%s"\n' $a $b

yields::

  a="foo bar" b="snafu"

while this::

  a=
  b=snafu
  print -f 'a="%s" b="%s"\n' $a $b

yields::

  a="snafu" b=""

roman-neuhauser/git-grope,roman-neuhauser/git-grope,roman-neuhauser/git-grope