patch 9.0.1392: using NULL pointer with nested :open command

Problem:    Using NULL pointer with nested :open command.
Solution:   Check that ccline.cmdbuff is not NULL.
diff --git a/src/testdir/term_util.vim b/src/testdir/term_util.vim
index 0f03731..88e2b33 100644
--- a/src/testdir/term_util.vim
+++ b/src/testdir/term_util.vim
@@ -55,6 +55,7 @@
 " "cols" - width of the terminal window (max. 78)
 " "statusoff" - number of lines the status is offset from default
 " "wait_for_ruler" - if zero then don't wait for ruler to show
+" "no_clean" - if non-zero then remove "--clean" from the command
 func RunVimInTerminal(arguments, options)
   " If Vim doesn't exit a swap file remains, causing other tests to fail.
   " Remove it here.
@@ -91,6 +92,10 @@
 
   let cmd = GetVimCommandCleanTerm() .. reset_u7 .. a:arguments
 
+  if get(a:options, 'no_clean', 0)
+    let cmd = substitute(cmd, '--clean', '', '')
+  endif
+
   let options = #{curwin: 1}
   if &termwinsize == ''
     let options.term_rows = rows
diff --git a/src/testdir/test_ex_mode.vim b/src/testdir/test_ex_mode.vim
index a660222..d03ec8f 100644
--- a/src/testdir/test_ex_mode.vim
+++ b/src/testdir/test_ex_mode.vim
@@ -134,6 +134,28 @@
   bwipe!
 endfunc
 
+" FIXME: this doesn't fail without the fix but hangs
+func Skip_Test_open_command_state()
+  " Tricky script that failed because State was not set properly
+  let lines =<< trim END
+      !ls ƒ
+      0scìi
+      so! Xsourced
+      set t_û0=0
+      v/-/o
+  END
+  call writefile(lines, 'XopenScript', '')
+
+  let sourced = ["!f\u0083\x02\<Esc>z=0"]
+  call writefile(sourced, 'Xsourced', 'b')
+
+  CheckRunVimInTerminal
+  let buf = RunVimInTerminal('-u NONE -i NONE -n -m -X -Z -e -s -S XopenScript -c qa!', #{rows: 6, wait_for_ruler: 0, no_clean: 1})
+  sleep 3
+
+  call StopVimInTerminal(buf)
+endfunc
+
 " Test for :g/pat/visual to run vi commands in Ex mode
 " This used to hang Vim before 8.2.0274.
 func Test_Ex_global()