vim-patch:8.2.0063: wrong size argument to vim_snprintf()

Problem:    Wrong size argument to vim_snprintf(). (Dominique Pelle)
Solution:   Reduce the size by the length. (related to vim/vim#5410)
08b28b7ad5

src/nvim/ops.c

@@ -5654,7 +5654,8 @@ void cursor_pos_info(dict_T *dict)
 
     bom_count = bomb_size();
     if (dict == NULL && bom_count > 0) {
-      vim_snprintf((char *)IObuff + STRLEN(IObuff), IOSIZE - STRLEN(IObuff),
+      const size_t len = STRLEN(IObuff);
+      vim_snprintf((char *)IObuff + len, IOSIZE - len,
                    _("(+%" PRId64 " for BOM)"), (int64_t)bom_count);
     }
     if (dict == NULL) {