Fixed race condition when timed-out link receives a late establishment proof a few milliseconds after it has timed out

RNS/Link.py

@@ -225,6 +225,7 @@ class Link:
         self.hash = self.link_id
 
     def handshake(self):
+        if self.status == Link.PENDING and self.prv != None:
             self.status = Link.HANDSHAKE
             self.shared_key = self.prv.exchange(self.peer_pub)
 
@@ -234,6 +235,8 @@ class Link:
                 salt=self.get_salt(),
                 context=self.get_context(),
             )
+        else:
+            RNS.log("Handshake attempt on "+str(self)+" with invalid state "+str(self.status), RNS.LOG_ERROR)
 
 
     def prove(self):