demo: fixed page build error resulted in broken page and uninitialised data use

src/examples2/demo.c

@@ -430,7 +430,7 @@ update_directory (void)
     update_cached_response (NULL);
     return;
   }
-  memcpy (rdc.buf, INDEX_PAGE_FOOTER, len);
+  memcpy (rdc.buf + rdc.off, INDEX_PAGE_FOOTER, len);
   rdc.off += len;
   initial_allocation = rdc.buf_len; /* remember for next time */
   response =