patch 9.1.1689: CmdlineChanged not triggered by <Del>

Problem:  CmdlineChanged not triggered by <Del>
Solution: Use STRCMP() instead of STRNCMP()
          (Shougo Matsushita)

closes: #18101

Signed-off-by: Shougo Matsushita <Shougo.Matsu@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>

src/testdir/test_autocmd.vim

@@ -2183,6 +2183,17 @@ func Test_Cmdline()
         \ '0abc1abc2abc3',
         \ ], g:log)
 
+  " <Del> should trigger CmdlineChanged
+  let g:log = []
+  call feedkeys(":foo\<Left>\<Left>\<Del>\<Del>\<Esc>", 'xt')
+  call assert_equal([
+        \ 'f',
+        \ 'fo',
+        \ 'foo',
+        \ 'fo',
+        \ 'f',
+        \ ], g:log)
+
   unlet g:log
   au! CmdlineChanged