We got check for nvram_len placed too early and the code never tried
reading CFE variables used on WGT634U. This is a regression introduced
in r45942 and reported in #20291.
Signed-off-by: Rafał Miłecki <zajec5@gmail.com>

Backport of r46584

git-svn-id: svn://svn.openwrt.org/openwrt/branches/chaos_calmer@46585 3c298f89-4303-0410-b956-a3cf2f4a3e73