bug#5973: Acknowledgement (Crash in get_next_display_element)

[David Reitter]

In line what is done just below in the same function, I would suggest at least 
the following change

diff --git a/src/xdisp.c b/src/xdisp.c
index 91fd06e..4fc4f56 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -5930,6 +5930,8 @@ get_next_display_element (it)
     {
       struct face *face = FACE_FROM_ID (it->f, it->face_id);
 
+      if (face) /* is face id valid? */
+       {
       if (it->what == IT_COMPOSITION && it->cmp_it.ch >= 0)
        {
          /* Automatic composition with glyph-string.   */
@@ -5945,6 +5947,7 @@ get_next_display_element (it)
 
          it->face_id = FACE_FOR_CHAR (it->f, face, it->c, pos, it->string);
        }
+       }
     }
 #endif