In previous patch (isearch_3.patch) the variables are not
restored because they were bind to the same symbol name, and
multi-isearch-end will set them to nil.

In addition, multi-isearch-end need to be added again to 
isearch-mode-end-hook, otherwise, even after exiting with C-g, C-s will 
start a multisearch instead of a normal isearch in the current buffer.

See attached patch: isearch_4.patch