patch 9.0.1726: incorrect heights in win_size_restore()

Problem: incorrect heights in win_size_restore()
Solution: avoid restoring incorrect heights in win_size_restore()

Changing 'showtabline' or 'cmdheight' in the cmdwin restores incorrect
window heights after closing the cmdwin.

This may produce a gap between the cmdline and the window above.

Solution: restore window sizes only if the number of lines available for windows
changed; subtract the rows of the tabline, cmdline and last window's statusline
from 'lines' (other statuslines don't matter).

closes: #12704

Signed-off-by: Christian Brabandt <cb@256bit.org>
Co-authored-by: Sean Dewar <seandewar@users.noreply.github.com>
diff --git a/src/proto/window.pro b/src/proto/window.pro
index 72612b8..cfb771d 100644
--- a/src/proto/window.pro
+++ b/src/proto/window.pro
@@ -81,6 +81,7 @@
 void command_height(void);
 void last_status(int morewin);
 int tabline_height(void);
+int last_stl_height(int morewin);
 int min_rows(void);
 int only_one_window(void);
 void check_lnums(int do_curwin);