patch 8.2.4074: going over the end of NameBuff

Problem:    Going over the end of NameBuff.
Solution:   Check length when appending a space.
diff --git a/src/testdir/test_edit.vim b/src/testdir/test_edit.vim
index e83d672..6322646 100644
--- a/src/testdir/test_edit.vim
+++ b/src/testdir/test_edit.vim
@@ -2103,5 +2103,20 @@
   bwipe!
 endfunc
 
+" Weird long file name was going over the end of NameBuff
+func Test_edit_overlong_file_name()
+  CheckUnix
+
+  file 0000000000000000000000000000
+  file %%%%%%%%%%%%%%%%%%%%%%%%%%
+  file %%%%%%
+  set readonly
+  set ls=2 
+
+  redraw!
+  set noreadonly ls&
+  bwipe!
+endfunc
+
 
 " vim: shiftwidth=2 sts=2 expandtab