tests/test-xdg.t

config: fix fm.data() handling of defaultvalue

This is a follow-up patch to rHG51a2e3102db2. This moves
`fm.data()` out of the if block in `commands.config()`.

Differential Revision: https://phab.mercurial-scm.org/D6720

#if no-windows no-osx

  $ mkdir -p xdgconf/hg
  $ echo '[ui]' > xdgconf/hg/hgrc
  $ echo 'username = foobar' >> xdgconf/hg/hgrc
  $ XDG_CONFIG_HOME="`pwd`/xdgconf" ; export XDG_CONFIG_HOME
  $ unset HGRCPATH
  $ hg config ui.username 2>/dev/null
  foobar

#endif