patch 9.1.1069: preinsert text completions not deleted with <C-W>/<C-U>

Problem:  preinsert text completions not deleted with <C-W>/<C-U>
          (ddad431, after v9.1.1059)
Solution: handle <C-W> or <C-U> specifically and clear the completion
          (glepnir)

fixes: #16557
closes: #16565

Signed-off-by: glepnir <glephunter@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/testdir/test_ins_complete.vim b/src/testdir/test_ins_complete.vim
index 49e4465..5d24d51 100644
--- a/src/testdir/test_ins_complete.vim
+++ b/src/testdir/test_ins_complete.vim
@@ -3103,6 +3103,14 @@
   call assert_equal("fo ", getline('.'))
   call assert_equal(3, col('.'))
 
+  call feedkeys("She\<C-X>\<C-N>\<C-U>", 'tx')
+  call assert_equal("", getline('.'))
+  call assert_equal(1, col('.'))
+
+  call feedkeys("She\<C-X>\<C-N>\<C-W>", 'tx')
+  call assert_equal("", getline('.'))
+  call assert_equal(1, col('.'))
+
   " whole line
   call feedkeys("Shello hero\<CR>\<C-X>\<C-L>", 'tx')
   call assert_equal("hello hero", getline('.'))