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.

1 files changed, 3 insertions, 2 deletions

diff --git a/src/xdisp.c b/src/xdisp.c
index cd3455aefcf..cc0a689ba32 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;