patch 9.0.0670: no space for command line when there is a tabline

Problem:    No space for command line when there is a tabline.
Solution:   Correct computation of where the command line should be.
            (closes #11295)

src/option.c

@@ -3577,7 +3577,8 @@ set_num_option(
 
 	// Only compute the new window layout when startup has been
 	// completed. Otherwise the frame sizes may be wrong.
-	if ((p_ch != old_value || topframe->fr_height != Rows - p_ch)
+	if ((p_ch != old_value
+		      || tabline_height() + topframe->fr_height != Rows - p_ch)
 		&& full_screen
 #ifdef FEAT_GUI
 		&& !gui.starting

src/testdir/dumps/Test_cmdheight_tabline_1.dump

@@ -0,0 +1,6 @@
+| +2&#ffffff0|[|N|o| |N|a|m|e|]| | +1&&@63
+> +0&&@74
+|~+0#4040ff13&| @73
+|~| @73
+|[+3#0000000&|N|o| |N|a|m|e|]| @47|0|,|0|-|1| @9|A|l@1
+| +0&&@74

src/testdir/test_cmdline.vim

@@ -287,6 +287,16 @@ func Test_changing_cmdheight()
   call StopVimInTerminal(buf)
 endfunc
 
+func Test_cmdheight_tabline()
+  CheckScreendump
+
+  let buf = RunVimInTerminal('-c "set ls=2" -c "set stal=2" -c "set cmdheight=1"', {'rows': 6})
+  call VerifyScreenDump(buf, 'Test_cmdheight_tabline_1', {})
+
+  " clean up
+  call StopVimInTerminal(buf)
+endfunc
+
 func Test_map_completion()
   call feedkeys(":map <unique> <si\<Tab>\<Home>\"\<CR>", 'xt')
   call assert_equal('"map <unique> <silent>', getreg(':'))

src/version.c

@@ -699,6 +699,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    670,
 /**/
     669,
 /**/

src/window.c

@@ -4332,7 +4332,7 @@ enter_tabpage(
     // When cmdheight is changed in a tab page with '<C-w>-', cmdline_row is
     // changed but p_ch and tp_ch_used are not changed. Thus we also need to
     // check cmdline_row.
-    if ((row < cmdline_row) && (cmdline_row <= Rows - p_ch))
+    if (row < cmdline_row && cmdline_row <= Rows - p_ch)
 	clear_cmdline = TRUE;
 
     // The tabpage line may have appeared or disappeared, may need to resize
@@ -6665,7 +6665,7 @@ command_height(void)
 	return;
 
     // Update cmdline_row to what it should be: just below the last window.
-    cmdline_row = topframe->fr_height;
+    cmdline_row = topframe->fr_height + tabline_height();
 
     // If cmdline_row is smaller than what it is supposed to be for 'cmdheight'
     // then set old_p_ch to what it would be, so that the windows get resized