patch 8.2.3476: renaming a buffer on startup may cause using freed memory

Problem:    Renaming a buffer on startup may cause using freed memory.
Solution:   Check if the buffer is used in a window. (closes #8955)
diff --git a/src/testdir/test_startup.vim b/src/testdir/test_startup.vim
index 6b64adf..897492d 100644
--- a/src/testdir/test_startup.vim
+++ b/src/testdir/test_startup.vim
@@ -1296,4 +1296,18 @@
   call delete('Xresult')
 endfunc
 
+func Test_rename_buffer_on_startup()
+  let lines =<< trim END
+      call writefile(['done'], 'Xresult')
+      qa!
+  END
+  call writefile(lines, 'Xscript')
+  if RunVim([], [], "--clean -e -s --cmd 'file x|new|file x' --cmd 'so Xscript'")
+    call assert_equal(['done'], readfile('Xresult'))
+  endif
+  call delete('Xscript')
+  call delete('Xresult')
+endfunc
+
+
 " vim: shiftwidth=2 sts=2 expandtab