vim-patch:8.2.4298: divide by zero with huge tabstop value

Problem:    Divide by zero with huge tabstop value.
Solution:   Reject tabstop value that overflows to zero.
fc88df42f1

src/nvim/testdir/test_vartabs.vim

@@ -135,6 +135,16 @@ func Test_vartabs()
   bwipeout!
 endfunc
 
+func Test_retab_invalid_arg()
+  new
+  call setline(1, "\ttext")
+  retab 0
+  call assert_fails("retab -8", 'E487: Argument must be positive')
+  call assert_fails("retab 10000", 'E475:')
+  call assert_fails("retab 720575940379279360", 'E475:')
+  bwipe!
+endfunc
+
 func! Test_vartabs_breakindent()
   if !exists("+breakindent")
     return