Mark some data during drag-and-drop

It doesn't make sense to prevent the return frame or movement
frame from being deleted, but we should at least protect them
from garbage collection.

* src/alloc.c (garbage_collect): Call mark_xterm.
* src/xterm.c (x_dnd_begin_drag_and_drop)
(x_dnd_cleanup_drag_and_drop): Clear movement and return frames
upon DND completion.
(mark_xterm): Mark those frames.
* src/xterm.h: Update prototypes.

1 files changed, 4 insertions, 0 deletions

diff --git a/src/alloc.c b/src/alloc.c
index 6d91ec33585..733f7733fa9 100644
--- a/src/alloc.c
+++ b/src/alloc.c
@@ -6196,6 +6196,10 @@ garbage_collect (void)
   mark_fringe_data ();
 #endif
 
+#ifdef HAVE_X_WINDOWS
+  mark_xterm ();
+#endif
+
   /* Everything is now marked, except for the data in font caches,
      undo lists, and finalizers.  The first two are compacted by
      removing an items which aren't reachable otherwise.  */