search("foo","") trigs the rtldebug fatal "string_search did a bobo!"

Imported from http://bugzilla.roxen.com/bugzilla/show_bug.cgi?id=2433

Reported by Martin Stjernholm mast@roxen.com

Searching for the empty string with search() trigs the rtldebug fatal "string_search did a bobo!"

Test case checked into 7.3, but problem also exists in 7.2.