Fix object key leak on insertion failure

tests/test_object_add_failure.c

@@ -0,0 +1,44 @@
+#ifdef NDEBUG
+#undef NDEBUG
+#endif
+#include <assert.h>
+#include <limits.h>
+#include <stdio.h>
+
+#include "json.h"
+
+static void check_insert_failure(const char *key, unsigned int opts)
+{
+	struct json_object *object = json_object_new_object();
+	struct json_object *value = json_object_new_int(7);
+	struct lh_table *table;
+	int saved_count;
+	int saved_size;
+
+	assert(object != NULL);
+	assert(value != NULL);
+	table = json_object_get_object(object);
+	assert(table != NULL);
+
+	/* Force lh_table_insert_w_hash() to reject the new entry. */
+	saved_count = table->count;
+	saved_size = table->size;
+	table->count = INT_MAX;
+	table->size = INT_MAX;
+
+	assert(json_object_object_add_ex(object, key, value,
+	                                 opts | JSON_C_OBJECT_ADD_KEY_IS_NEW) == -1);
+
+	table->count = saved_count;
+	table->size = saved_size;
+	json_object_put(value);
+	json_object_put(object);
+}
+
+int main(void)
+{
+	check_insert_failure("copied-key", 0);
+	check_insert_failure("constant-key", JSON_C_OBJECT_ADD_CONSTANT_KEY);
+	puts("PASS");
+	return 0;
+}