fix crash when can't find a CID and timeout hits

the exception was not raised, thus a Nil was returned that was
than wrapped in an option, leading to crash.


Signed-off-by: Csaba Kiraly <csaba.kiraly@gmail.com>

codex/blockexchange/engine/pendingblocks.nim

@@ -48,6 +48,8 @@ proc getWantHandle*(
     raise exc
   except CatchableError as exc:
     trace "Pending WANT failed or expired", exc = exc.msg
+    # no need to cancel, it is already cancelled by wait()
+    raise exc
   finally:
     p.blocks.del(cid)