master 30cd8045d7: Fix pdumper build

[Po Lu]

branch: master
commit 30cd8045d7bf6be772976f43891f9216182b552f
Author: Po Lu <luangruo@yahoo.com>
Commit: Po Lu <luangruo@yahoo.com>

    Fix pdumper build
    
    * src/xselect.c (mark_xselect): Don't mark if
    outstanding_transfers.next is still NULL.
---
 src/xselect.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/src/xselect.c b/src/xselect.c
index c635f84065..c23cda1f66 100644
--- a/src/xselect.c
+++ b/src/xselect.c
@@ -3415,6 +3415,11 @@ mark_xselect (void)
      request stack or the list of outstanding transfers.  */
 
   next = outstanding_transfers.next;
+
+  if (!next)
+    /* syms_of_xselect has not yet been called.  */
+    return;
+
   while (next != &outstanding_transfers)
     {
       mark_object (next->data.string);