patch 9.1.1043: [security]: segfault in win_line()

Problem:  [security]: segfault in win_line()
          (fizz-is-on-the-way)
Solution: Check that ScreenLines is not NULL

Github Advisory:
https://github.com/vim/vim/security/advisories/GHSA-j3g9-wg22-v955

Signed-off-by: Christian Brabandt <cb@256bit.org>

src/gui.c

@@ -4478,13 +4478,15 @@ gui_do_scroll(void)
     /*
      * Don't call updateWindow() when nothing has changed (it will overwrite
      * the status line!).
+     *
+     * Check for ScreenLines, because in ex-mode, we don't have a valid display.
      */
-    if (old_topline != wp->w_topline
+    if (ScreenLines != NULL && (old_topline != wp->w_topline
 	    || wp->w_redr_type != 0
 #ifdef FEAT_DIFF
 	    || old_topfill != wp->w_topfill
 #endif
-	    )
+	    ))
     {
 	int type = UPD_VALID;
 

src/testdir/crash/ex_redraw_crash

@@ -0,0 +1 @@
+vdivvi|gIv|÷<>X<><58>\<5C><>,X<><58>X<EFBFBD><58>\<5C><>#

src/testdir/test_crash.vim

@@ -234,6 +234,12 @@ func Test_crash1_3()
   call term_sendkeys(buf, args)
   call TermWait(buf, 50)
 
+  let file = 'crash/ex_redraw_crash'
+  let cmn_args = "%s -u NONE -i NONE -n -m -X -Z -e -s -S %s -c ':qa!'"
+  let args = printf(cmn_args, vim, file)
+  call term_sendkeys(buf, args)
+  call TermWait(buf, 150)
+
   " clean up
   exe buf .. "bw!"
   bw!

src/version.c

@@ -704,6 +704,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1043,
 /**/
     1042,
 /**/