git_config_*: don't assume we are parsing a config file
git_config_*: don't assume we are parsing a config file

These functions get called by other code, including parsing
config options from the command line. In that case,
config_file_name is NULL, leading to an ugly message or even
a segfault on some implementations of printf.

Signed-off-by: Jeff King <696e3fbcf235d40b6ea1ebd61c87cbea79d444e7@peff.net>
Signed-off-by: Junio C Hamano <a6723cc3f76163bf7adb636a73ac3b0ceb3e6b9b@pobox.com>

destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git