vim-patch:8.2.4563: "z=" in Visual mode may go beyond the end of the line

Problem:    "z=" in Visual mode may go beyond the end of the line.
Solution:   Adjust "badlen".

5c68617d39

Co-authored-by: Bram Moolenaar <Bram@vim.org>

src/nvim/spellsuggest.c

@@ -483,6 +483,11 @@ void spell_suggest(int count)
     }
     badlen++;
     end_visual_mode();
+    // make sure we don't include the NUL at the end of the line
+    line = get_cursor_line_ptr();
+    if (badlen > (int)strlen(line) - (int)curwin->w_cursor.col) {
+      badlen = (int)strlen(line) - (int)curwin->w_cursor.col;
+    }
     // Find the start of the badly spelled word.
   } else if (spell_move_to(curwin, FORWARD, true, true, NULL) == 0
              || curwin->w_cursor.col > prev_cursor.col) {

src/nvim/testdir/test_spell.vim

@@ -531,8 +531,23 @@ func Test_spellsuggest_timeout()
   call assert_fails('set spellsuggest=timeout:--9', 'E474:')
 endfunc
 
+func Test_spellsuggest_visual_end_of_line()
+  let enc_save = &encoding
+  " set encoding=iso8859
+
+  " This was reading beyond the end of the line.
+  norm R00000000000
+  sil norm 0
+  sil! norm i00000)
+  sil! norm i00000)
+  call feedkeys("\<CR>")
+  norm z=
+
+  let &encoding = enc_save
+endfunc
+
 func Test_spellinfo()
-  throw 'skipped: Nvim does not support enc=latin1'
+  throw 'Skipped: Nvim does not support enc=latin1'
   new
   let runtime = substitute($VIMRUNTIME, '\\', '/', 'g')