config.c: refactor die_bad_number() to not call gettext() early

config.c: refactor die_bad_number() to not call gettext() early

Prepare die_bad_number() for a change to specially handle
GIT_TEST_GETTEXT_POISON calling git_env_bool() by making
die_bad_number() not call gettext() early, which would in turn call
git_env_bool().

There's no meaningful change here yet, just a re-arrangement of the
current code to make that subsequent change easier to read.

Signed-off-by: Ævar Arnfjörð Bjarmason <redacted>
Signed-off-by: Junio C Hamano <redacted>