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
pager.pager=p0 # $TESTTMP/sysrc:4
ui.editor=e1 # $TESTTMP/userrc:2
pager.pager=p2 # $PAGER
ui.editor=e1 # $TESTTMP/userrc:2