com_err: correctly deal with lack of libintl

com_err: correctly deal with lack of libintl

On machines lacking a libintl, _intlize() currently fails to initialize
the output error string--leading to tools (e.g., translate_et) returning
a null string; make afs_com_err fall back to returning the en/US canonical
error text when we don't have any i18n support...

Change-Id: I333745fb0a16e5bc9adb0755591d80de010d4d31
Reviewed-on: http://gerrit.openafs.org/6638
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementix.org>