Tweak last font-related changes to fix bug#15686.

* alloc.c (mark_object) [HAVE_WINDOW_SYSTEM]: If marked frame
is a live window system frame, mark it's default font too.

src/ChangeLog

+2013-10-23  Dmitry Antipov  <dmantipov@yandex.ru>
+
+	Tweak last font-related changes to fix bug#15686.
+	* alloc.c (mark_object) [HAVE_WINDOW_SYSTEM]: If marked frame
+	is a live window system frame, mark it's default font too.
+
 2013-10-23  Glenn Morris  <rgm@gnu.org>
 
 	* Makefile.in (RUN_TEMACS): Make relative (again).

src/alloc.c

@@ -5951,8 +5951,21 @@ mark_object (Lisp_Object arg)
 	    break;
 
 	  case PVEC_FRAME:
-	    mark_vectorlike (ptr);
-	    mark_face_cache (((struct frame *) ptr)->face_cache);
+	    {
+	      struct frame *f = (struct frame *) ptr;
+
+	      mark_vectorlike (ptr);
+	      mark_face_cache (f->face_cache);
+#ifdef HAVE_WINDOW_SYSTEM
+	      if (FRAME_WINDOW_P (f) && FRAME_X_OUTPUT (f))
+		{
+		  struct font *font = FRAME_FONT (f);
+
+		  if (font && !VECTOR_MARKED_P (font))
+		    mark_vectorlike ((struct Lisp_Vector *) font);
+		}
+#endif
+	    }
 	    break;
 
 	  case PVEC_WINDOW: