patch 7.4.1834

Problem:    Possible crash when conceal is active.
Solution:   Check for the screen to be valid when redrawing a line.

src/screen.c

@@ -801,6 +801,10 @@ update_single_line(win_T *wp, linenr_T lnum)
     int		row;
     int		j;
 
+    /* Don't do anything if the screen structures are (not yet) valid. */
+    if (!screen_valid(TRUE))
+	return;
+
     if (lnum >= wp->w_topline && lnum < wp->w_botline
 				 && foldedCount(wp, lnum, &win_foldinfo) == 0)
     {

src/version.c

@@ -753,6 +753,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1834,
 /**/
     1833,
 /**/