patch 9.1.0579: Ex command is still executed after giving E1247

Problem:  Ex command is still executed after giving E1247.
Solution: Indicate the error properly and set cmd to NULL.
          (zeertzjq)

closes: #15241

Signed-off-by: zeertzjq <zeertzjq@outlook.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/testdir/test_excmd.vim b/src/testdir/test_excmd.vim
index 221ceb0..3b7e489 100644
--- a/src/testdir/test_excmd.vim
+++ b/src/testdir/test_excmd.vim
@@ -703,6 +703,8 @@
   call setline(1, range(100))
   call assert_fails('|.44444444444444444444444', 'E1247:')
   call assert_fails('|.9223372036854775806', 'E1247:')
+  call assert_fails('.44444444444444444444444d', 'E1247:')
+  call assert_equal(range(100)->map('string(v:val)'), getline(1, '$'))
 
   $
   yank 77777777777777777777