Fix crash with adding internal ignores

Depending on what you had done before adding new items to the
internal ignores list, it was possible for the cache of ignore
data to be uninitialized.

src/ignore.c

@@ -205,6 +205,16 @@ cleanup:
 	return 0;
 }
 
+static int get_internal_ignores(git_attr_file **ign, git_repository *repo)
+{
+	int error;
+
+	if (!(error = git_attr_cache__init(repo)))
+		error = git_attr_cache__internal_file(repo, GIT_IGNORE_INTERNAL, ign);
+
+	return error;
+}
+
 int git_ignore_add_rule(
 	git_repository *repo,
 	const char *rules)
@@ -212,10 +222,7 @@ int git_ignore_add_rule(
 	int error;
 	git_attr_file *ign_internal;
 
-	error = git_attr_cache__internal_file(
-		repo, GIT_IGNORE_INTERNAL, &ign_internal);
-
-	if (!error && ign_internal != NULL)
+	if (!(error = get_internal_ignores(&ign_internal, repo)))
 		error = parse_ignore_file(repo, rules, ign_internal);
 
 	return error;
@@ -227,10 +234,7 @@ int git_ignore_clear_internal_rules(
 	int error;
 	git_attr_file *ign_internal;
 
-	error = git_attr_cache__internal_file(
-		repo, GIT_IGNORE_INTERNAL, &ign_internal);
-
-	if (!error && ign_internal != NULL)
+	if (!(error = get_internal_ignores(&ign_internal, repo)))
 		git_attr_file__clear_rules(ign_internal);
 
 	return error;

tests-clar/status/ignore.c

@@ -199,3 +199,18 @@ void test_status_ignore__adding_internal_ignores(void)
 	cl_git_pass(git_status_should_ignore(&ignored, g_repo, "two.bar"));
 	cl_assert(ignored);
 }
+
+void test_status_ignore__add_internal_as_first_thing(void)
+{
+	int ignored;
+	const char *add_me = "\n#################\n## Eclipse\n#################\n\n*.pydevproject\n.project\n.metadata\nbin/\ntmp/\n*.tmp\n\n";
+
+	g_repo = cl_git_sandbox_init("empty_standard_repo");
+
+	cl_git_pass(git_ignore_add_rule(g_repo, add_me));
+
+	cl_git_pass(git_status_should_ignore(&ignored, g_repo, "one.tmp"));
+	cl_assert(ignored);
+	cl_git_pass(git_status_should_ignore(&ignored, g_repo, "two.bar"));
+	cl_assert(!ignored);
+}