master ac45f31: Fix dangerous code in xdisp.c

[Eli Zaretskii]

branch: master
commit ac45f314547ed9904ddc387157d3f4ba0c5fe1d2
Author: Eli Zaretskii <eliz@gnu.org>
Commit: Eli Zaretskii <eliz@gnu.org>

    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.
---
 src/xdisp.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/src/xdisp.c b/src/xdisp.c
index cd3455a..cc0a689 100644
--- 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;