patch 8.1.1242: no cmdline redraw when tabpages have different 'cmdheight'

Problem:    No cmdline redraw when tabpages have different 'cmdheight'.
Solution:   redraw the command line when 'cmdheight' changes when switching
            tabpages. (closes #4321)
diff --git a/src/testdir/screendump.vim b/src/testdir/screendump.vim
index 9687dc8..50e3384 100644
--- a/src/testdir/screendump.vim
+++ b/src/testdir/screendump.vim
@@ -26,6 +26,7 @@
 " Options is a dictionary, these items are recognized:
 " "rows" - height of the terminal window (max. 20)
 " "cols" - width of the terminal window (max. 78)
+" "statusoff" - number of lines the status is offset from default
 func RunVimInTerminal(arguments, options)
   " If Vim doesn't exit a swap file remains, causing other tests to fail.
   " Remove it here.
@@ -51,6 +52,7 @@
   " Make the window 20 lines high and 75 columns, unless told otherwise.
   let rows = get(a:options, 'rows', 20)
   let cols = get(a:options, 'cols', 75)
+  let statusoff = get(a:options, 'statusoff', 1)
 
   let cmd = GetVimCommandClean()
 
@@ -77,7 +79,7 @@
   " using valgrind).
   " If it fails then show the terminal contents for debugging.
   try
-    call WaitFor({-> len(term_getline(buf, rows)) >= cols - 1 || len(term_getline(buf, rows - 1)) >= cols - 1})
+    call WaitFor({-> len(term_getline(buf, rows)) >= cols - 1 || len(term_getline(buf, rows - statusoff)) >= cols - 1})
   catch /timed out after/
     let lines = map(range(1, rows), {key, val -> term_getline(buf, val)})
     call assert_report('RunVimInTerminal() failed, screen contents: ' . join(lines, "<NL>"))