patch 9.0.0018: going over the end of the typahead

Problem:    Going over the end of the typahead.
Solution:   Put a NUL after the typeahead.
diff --git a/src/testdir/test_mapping.vim b/src/testdir/test_mapping.vim
index ace6453..2927ba7 100644
--- a/src/testdir/test_mapping.vim
+++ b/src/testdir/test_mapping.vim
@@ -1715,4 +1715,14 @@
   call delete('Xtest_map_after_timed_out_nop')
 endfunc
 
+func Test_using_past_typeahead()
+  nnoremap :00 0
+  exe "norm :set \x80\xfb0=0\<CR>"
+  exe "sil norm :0\x0f\<C-U>\<CR>"
+
+  exe "norm :set \x80\xfb0=\<CR>"
+  nunmap :00
+endfunc
+
+
 " vim: shiftwidth=2 sts=2 expandtab