Fix dangerous code in xdisp.c

* src/xdisp.c (move_it_to, display_line): Make sure ZV_BYTE is
greater than 1 before fetching previous byte.

diff --git a/src/xdisp.c b/src/xdisp.c
index cd3455aefcf806c80f69b37864bb38844c1428cd..cc0a689ba32e9ff449b998801ba010dfc713fb24 100644 (file)
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -10052,7 +10052,7 @@ move_it_to (struct it *it, ptrdiff_t to_charpos, int to_x, int to_y, int to_vpos
              && (IT_CHARPOS (*it) > to_charpos
                  || (IT_CHARPOS (*it) == to_charpos
                      && to_charpos == ZV
-                     && FETCH_BYTE (ZV_BYTE - 1) != '\n')))
+                     && (ZV_BYTE <= 1 || FETCH_BYTE (ZV_BYTE - 1) != '\n'))))
            {
              reached = 9;
              goto out;
@@ -24118,7 +24118,8 @@ display_line (struct it *it, int cursor_vpos)
             the logical order.  */
          if (IT_BYTEPOS (*it) > BEG_BYTE)
            row->ends_at_zv_p =
-             IT_BYTEPOS (*it) >= ZV_BYTE && FETCH_BYTE (ZV_BYTE - 1) != '\n';
+             IT_BYTEPOS (*it) >= ZV_BYTE
+             && (ZV_BYTE <= 1 || FETCH_BYTE (ZV_BYTE - 1) != '\n');
          else
            row->ends_at_zv_p = false;
          break;