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
#require test-repo jshint hg10
$ . "$TESTDIR/helpers-testrepo.sh"
run jshint on all tracked files ending in .js except vendored dependencies
$ cd "`dirname "$TESTDIR"`"
$ testrepohg locate 'set:**.js' \
> 2>/dev/null \
> | xargs jshint