Always set *nongit_ok in setup_git_directory_gently()

setup_git_directory_gently() only modified the value of its *nongit_ok
argument if we were not in a git repository.  Now it will always set it
to 0 when we are inside a repository.

Also remove now unnecessary initializations in the callers of this
function.

Signed-off-by: SZEDER Gábor <szeder@ira.uka.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/builtin-config.c b/builtin-config.c
index 2b9a426..c34bc8b 100644
--- a/builtin-config.c
+++ b/builtin-config.c
@@ -264,7 +264,7 @@
 
 int cmd_config(int argc, const char **argv, const char *prefix)
 {
-	int nongit = 0;
+	int nongit;
 	char* value;
 	const char *file = setup_git_directory_gently(&nongit);