bplist: Check for invalid ref_size in bplist trailer
diff --git a/src/bplist.c b/src/bplist.c
index 7ab9380..7cc8a03 100644
--- a/src/bplist.c
+++ b/src/bplist.c
@@ -727,6 +727,9 @@
     if (offset_size == 0)
         return;
 
+    if (ref_size == 0)
+        return;
+
     if (root_object >= num_objects)
         return;