patch 8.1.1709: Coverity warns for possibly using a NULL pointer

Problem:    Coverity warns for possibly using a NULL pointer.
Solution:   Make sure no NULL pointer is used.

Author: brammool

src/popupwin.c

@@ -516,25 +516,24 @@ apply_general_options(win_T *wp, dict_T *dict)
     di = dict_find(dict, (char_u *)"borderhighlight", -1);
     if (di != NULL)
     {
-	if (di->di_tv.v_type != VAR_LIST)
+	if (di->di_tv.v_type != VAR_LIST || di->di_tv.vval.v_list == NULL)
 	    emsg(_(e_listreq));
 	else
 	{
 	    list_T	*list = di->di_tv.vval.v_list;
 	    listitem_T	*li;
 	    int		i;
 
-	    if (list != NULL)
-		for (i = 0, li = list->lv_first; i < 4 && i < list->lv_len;
-							 ++i, li = li->li_next)
-		{
-		    str = tv_get_string(&li->li_tv);
-		    if (*str != NUL)
-			wp->w_border_highlight[i] = vim_strsave(str);
-		}
+	    for (i = 0, li = list->lv_first; i < 4 && i < list->lv_len;
+						     ++i, li = li->li_next)
+	    {
+		str = tv_get_string(&li->li_tv);
+		if (*str != NUL)
+		    wp->w_border_highlight[i] = vim_strsave(str);
+	    }
 	    if (list->lv_len == 1 && wp->w_border_highlight[0] != NULL)
 		for (i = 1; i < 4; ++i)
-			wp->w_border_highlight[i] =
+		    wp->w_border_highlight[i] =
 					vim_strsave(wp->w_border_highlight[0]);
 	}
     }

src/testdir/test_popupwin.vim

@@ -634,6 +634,8 @@ func Test_popup_invalid_arguments()
   call popup_clear()
   call assert_fails('call popup_create("text", #{borderhighlight: "none"})', 'E714:')
   call popup_clear()
+  call assert_fails('call popup_create("text", #{borderhighlight: test_null_list()})', 'E714:')
+  call popup_clear()
   call assert_fails('call popup_create("text", #{borderchars: "none"})', 'E714:')
   call popup_clear()
 

src/version.c

@@ -777,6 +777,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1709,
 /**/
     1708,
 /**/