tree-cache: Don't segfault upon corruption

src/tree-cache.c

@@ -178,9 +178,12 @@ void git_tree_cache_free(git_tree_cache *tree)
 	if (tree == NULL)
 		return;
 
-	for (i = 0; i < tree->children_count; ++i)
-		git_tree_cache_free(tree->children[i]);
+	if (tree->children != NULL) {
+		for (i = 0; i < tree->children_count; ++i)
+			git_tree_cache_free(tree->children[i]);
+
+		git__free(tree->children);
+	}
 
-	git__free(tree->children);
 	git__free(tree);
 }

tests/index/tests.c

@@ -6,6 +6,7 @@ static const size_t index_entry_count_2 = 1437;
 #define TEST_INDEX_PATH cl_fixture("testrepo.git/index")
 #define TEST_INDEX2_PATH cl_fixture("gitgit.index")
 #define TEST_INDEXBIG_PATH cl_fixture("big.index")
+#define TEST_INDEXBAD_PATH cl_fixture("bad.index")
 
 
 /* Suite data */
@@ -535,3 +536,11 @@ void test_index_tests__reload_from_disk(void)
 	git_index_free(write_index);
 	git_repository_free(repo);
 }
+
+void test_index_tests__corrupted_extension(void)
+{
+	/* sort the entires in an empty index */
+	git_index *index;
+
+	cl_git_fail_with(git_index_open(&index, TEST_INDEXBAD_PATH), GIT_ERROR);
+}