UI: only wrap cursor motion horizontally when dragging markers

It's not useful to wrap vertical motion when dragging markers.
It was too easy to accidentally wrap the cursor to the top of a region,
as markers need to be dragged from the bottom edge of the region.

source/blender/editors/animation/anim_markers.c

@@ -1037,7 +1037,7 @@ static void MARKER_OT_move(wmOperatorType *ot)
   ot->cancel = ed_marker_move_cancel;
 
   /* flags */
-  ot->flag = OPTYPE_REGISTER | OPTYPE_UNDO | OPTYPE_BLOCKING | OPTYPE_GRAB_CURSOR_XY;
+  ot->flag = OPTYPE_REGISTER | OPTYPE_UNDO | OPTYPE_BLOCKING | OPTYPE_GRAB_CURSOR_X;
 
   /* rna storage */
   RNA_def_int(ot->srna, "frames", 0, INT_MIN, INT_MAX, "Frames", "", INT_MIN, INT_MAX);