Fix heap buffer overflow

Fixes #800

cJSON.c

@@ -1660,6 +1660,11 @@ static cJSON_bool parse_object(cJSON * const item, parse_buffer * const input_bu
             current_item = new_item;
         }
 
+        if (cannot_access_at_index(input_buffer, 1))
+        {
+            goto fail; /* nothing comes after the comma */
+        }
+
         /* parse the name of the child */
         input_buffer->offset++;
         buffer_skip_whitespace(input_buffer);