patch 9.0.1491: wrong scrolling with ls=0 and :botright split

Problem:    Wrong scrolling with ls=0 and :botright split.
Solution:   Add statusline before calling frame_new_height(). (closes #12299)

src/testdir/test_window_cmd.vim

@@ -19,6 +19,24 @@ func Test_window_cmd_ls0_with_split()
   set ls&vim
 endfunc
 
+func Test_window_cmd_ls0_split_scrolling()
+  CheckRunVimInTerminal
+
+  let lines =<< trim END
+    set laststatus=0
+    call setline(1, range(1, 100))
+    normal! G
+  END
+  call writefile(lines, 'XTestLs0SplitScrolling', 'D')
+  let buf = RunVimInTerminal('-S XTestLs0SplitScrolling', #{rows: 10})
+
+  call term_sendkeys(buf, ":botright split\<CR>")
+  call WaitForAssert({-> assert_match('Bot$', term_getline(buf, 5))})
+  call assert_equal('100', term_getline(buf, 4))
+
+  call StopVimInTerminal(buf)
+endfunc
+
 func Test_window_cmd_cmdwin_with_vsp()
   let efmt = 'Expected 0 but got %d (in ls=%d, %s window)'
   for v in range(0, 2)

src/version.c

@@ -695,6 +695,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1491,
 /**/
     1490,
 /**/

src/window.c

@@ -1307,6 +1307,7 @@ win_split_ins(
 	// "new_size" of the current window goes to the new window, use
 	// one row for the status line
 	win_new_height(wp, new_size);
+	int old_status_height = oldwin->w_status_height;
 	if (flags & (WSP_TOP | WSP_BOT))
 	{
 	    int new_fr_height = curfrp->fr_height - new_size
@@ -1314,6 +1315,8 @@ win_split_ins(
 
 	    if (!((flags & WSP_BOT) && p_ls == 0))
 		new_fr_height -= STATUS_HEIGHT;
+	    if (flags & WSP_BOT)
+		frame_add_statusline(curfrp);
 	    frame_new_height(curfrp, new_fr_height, flags & WSP_TOP, FALSE);
 	}
 	else
@@ -1328,12 +1331,10 @@ win_split_ins(
 	{
 	    wp->w_winrow = oldwin->w_winrow + VISIBLE_HEIGHT(oldwin)
 							       + STATUS_HEIGHT;
-	    wp->w_status_height = oldwin->w_status_height;
+	    wp->w_status_height = old_status_height;
 	    if (!(flags & WSP_BOT))
 		oldwin->w_status_height = STATUS_HEIGHT;
 	}
-	if (flags & WSP_BOT)
-	    frame_add_statusline(curfrp);
 	frame_fix_height(wp);
 	frame_fix_height(oldwin);
     }
@@ -3791,13 +3792,8 @@ frame_add_statusline(frame_T *frp)
     if (frp->fr_layout == FR_LEAF)
     {
 	wp = frp->fr_win;
-	if (wp->w_status_height == 0)
-	{
-	    if (wp->w_height > 0)	// don't make it negative
-		--wp->w_height;
 	wp->w_status_height = STATUS_HEIGHT;
     }
-    }
     else if (frp->fr_layout == FR_ROW)
     {
 	// Handle all the frames in the row.