patch 8.0.0643: when a pattern search is slow Vim becomes unusable

Problem:    When 'hlsearch' is set and matching with the last search pattern
            is very slow, Vim becomes unusable.  Cannot quit search by
            pressing CTRL-C.
Solution:   When the search times out set a flag and don't try again.  Check
            for timeout and CTRL-C in NFA loop that adds states.

src/gui.c

@@ -5361,7 +5361,7 @@ gui_do_findrepl(
 	    searchflags += SEARCH_START;
 	i = msg_scroll;
 	(void)do_search(NULL, down ? '/' : '?', ga.ga_data, 1L,
-							   searchflags, NULL);
+						      searchflags, NULL, NULL);
 	msg_scroll = i;	    /* don't let an error message set msg_scroll */
     }