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 <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

config.c

@@ -280,11 +280,18 @@ int git_parse_ulong(const char *value, unsigned long *ret)
 	return 0;
 }
 
+static void die_bad_config(const char *name)
+{
+	if (config_file_name)
+		die("bad config value for '%s' in %s", name, config_file_name);
+	die("bad config value for '%s'", name);
+}
+
 int git_config_int(const char *name, const char *value)
 {
 	long ret;
 	if (!git_parse_long(value, &ret))
-		die("bad config value for '%s' in %s", name, config_file_name);
+		die_bad_config(name);
 	return ret;
 }
 
@@ -292,7 +299,7 @@ unsigned long git_config_ulong(const char *name, const char *value)
 {
 	unsigned long ret;
 	if (!git_parse_ulong(value, &ret))
-		die("bad config value for '%s' in %s", name, config_file_name);
+		die_bad_config(name);
 	return ret;
 }