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.
diff --git a/src/ex_docmd.c b/src/ex_docmd.c
index bf340de..9dac9bf 100644
--- a/src/ex_docmd.c
+++ b/src/ex_docmd.c
@@ -4556,7 +4556,7 @@
 			curwin->w_cursor.col = 0;
 		    searchcmdlen = 0;
 		    if (!do_search(NULL, c, cmd, 1L,
-				       SEARCH_HIS | SEARCH_MSG, NULL))
+					  SEARCH_HIS | SEARCH_MSG, NULL, NULL))
 		    {
 			curwin->w_cursor = pos;
 			cmd = NULL;
@@ -4613,7 +4613,7 @@
 		    if (searchit(curwin, curbuf, &pos,
 				*cmd == '?' ? BACKWARD : FORWARD,
 				(char_u *)"", 1L, SEARCH_MSG,
-					i, (linenr_T)0, NULL) != FAIL)
+					i, (linenr_T)0, NULL, NULL) != FAIL)
 			lnum = pos.lnum;
 		    else
 		    {