Avoid crash on composition (backport from trunk).

* xdisp.c (fill_composite_glyph_string): Always set s->face, to
avoid a crash (bug#9496).

src/ChangeLog

+2011-11-11  Johan Bockgård  <bojohan@gnu.org>
+
+	* xdisp.c (fill_composite_glyph_string): Always set s->face, to
+	avoid a crash (bug#9496).
+
 2012-01-09  Chong Yidong  <cyd@gnu.org>
 
 	* xdisp.c (note_mouse_highlight): Fix use of uninitialized var.

src/xdisp.c

@@ -19635,6 +19635,12 @@ fill_composite_glyph_string (s, base_face, overlaps)
     }
   s->cmp_to = i;
 
+  if (s->face == NULL)
+    {
+      s->face = base_face->ascii_face;
+      s->font = s->face->font;
+    }
+
   /* All glyph strings for the same composition has the same width,
      i.e. the width set for the first component of the composition.  */
   s->width = s->first_glyph->pixel_width;