patch 9.0.2109: [security]: overflow in nv_z_get_count

Problem:  [security]: overflow in nv_z_get_count
Solution: break out, if count is too large

When getting the count for a normal z command, it may overflow for large
counts given. So verify, that we can safely store the result in a long.

Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/testdir/test_normal.vim b/src/testdir/test_normal.vim
index c7d37f0..6b889f4 100644
--- a/src/testdir/test_normal.vim
+++ b/src/testdir/test_normal.vim
@@ -4159,4 +4159,9 @@
   bw!
 endfunc
 
+func Test_normal34_zet_large()
+  " shouldn't cause overflow
+  norm! z9765405999999999999
+endfunc
+
 " vim: shiftwidth=2 sts=2 expandtab