patch 8.2.5148: invalid memory access when using expression on command line

Problem:    Invalid memory access when using an expression on the command line.
Solution:   Make sure the position does not go negative.
diff --git a/src/testdir/test_cmdline.vim b/src/testdir/test_cmdline.vim
index 2289c34..9c08d13 100644
--- a/src/testdir/test_cmdline.vim
+++ b/src/testdir/test_cmdline.vim
@@ -1987,6 +1987,11 @@
   call assert_equal("\"e \<C-\>\<C-Y>", @:)
 endfunc
 
+" This was making the insert position negative
+func Test_cmdline_expr_register()
+  exe "sil! norm! ?\<C-\>e0\<C-R>0\<Esc>?\<C-\>e0\<CR>"
+endfunc
+
 " Test for 'imcmdline' and 'imsearch'
 " This test doesn't actually test the input method functionality.
 func Test_cmdline_inputmethod()