[PATCH] config: fix several access(NULL) calls

[Matthieu Moy <Matthieu.Moy@imag.fr>]

When $HOME is unset, home_config_paths fails and returns NULL pointers
for user_config and xdg_config. Valgrind complains with Syscall param
access(pathname) points to unaddressable byte(s).

Don't call blindly access() on these variables, but test them for
NULL-ness before.

Signed-off-by: Matthieu Moy <Matthieu.Moy@imag.fr>
---
> This patch causes valgrind warnings in t1300.81 (get --path copes with
> unset $HOME) about passing NULL to access():

Indeed. The following patch should fix it.

 builtin/config.c | 3 ++-
 config.c         | 4 ++--
 2 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/builtin/config.c b/builtin/config.c
index e8e1c0a..67945b2 100644
--- a/builtin/config.c
+++ b/builtin/config.c
@@ -387,7 +387,8 @@ int cmd_config(int argc, const char **argv, const char *prefix)
 
 		home_config_paths(&user_config, &xdg_config, "config");
 
-		if (access(user_config, R_OK) && !access(xdg_config, R_OK))
+		if (user_config && access(user_config, R_OK) &&
+		    xdg_config && !access(xdg_config, R_OK))
 			given_config_file = xdg_config;
 		else if (user_config)
 			given_config_file = user_config;
diff --git a/config.c b/config.c
index d28a499..6b97503 100644
--- a/config.c
+++ b/config.c
@@ -940,12 +940,12 @@ int git_config_early(config_fn_t fn, void *data, const char *repo_config)
 		found += 1;
 	}
 
-	if (!access(xdg_config, R_OK)) {
+	if (xdg_config && !access(xdg_config, R_OK)) {
 		ret += git_config_from_file(fn, xdg_config, data);
 		found += 1;
 	}
 
-	if (!access(user_config, R_OK)) {
+	if (user_config && !access(user_config, R_OK)) {
 		ret += git_config_from_file(fn, user_config, data);
 		found += 1;
 	}
-- 
1.7.11.1.29.g0e8593d.dirty