(mirror_line_dance): Avoid crash if W2 is null.

1 files changed, 14 insertions, 8 deletions

diff --git a/src/dispnew.c b/src/dispnew.c
index 5ffd1a2ce58..4f29abdb389 100644
--- a/src/dispnew.c
+++ b/src/dispnew.c
@@ -3165,14 +3165,20 @@ mirror_line_dance (w, unchanged_at_top, nlines, copy_from, retained_p)
                   int m2_from;
 
                   w2 = frame_row_to_window (root, frame_from);
-                  m2 = w2->current_matrix;
-                  m2_from = frame_from - m2->matrix_y;
-                  copy_row_except_pointers (m->rows + window_to,
-                                            m2->rows + m2_from);
-
-                  /* If frame line is empty, window line is empty, too.  */
-                  if (!retained_p[copy_from[i]])
-                    m->rows[window_to].enabled_p = 0;
+                  /* ttn@surf.glug.org: when enabling menu bar using `emacs
+                     -nw', FROM_FRAME sometimes has no associated window.
+                     This check avoids a segfault if W2 is null.  */
+                  if (w2)
+                    {
+                      m2 = w2->current_matrix;
+                      m2_from = frame_from - m2->matrix_y;
+                      copy_row_except_pointers (m->rows + window_to,
+                                                m2->rows + m2_from);
+
+                      /* If frame line is empty, window line is empty, too.  */
+                      if (!retained_p[copy_from[i]])
+                        m->rows[window_to].enabled_p = 0;
+                    }
                   sync_p = 1;
                 }
               else if (from_inside_window_p)