Prop. 159: Clarify csz may be 0 in relay response from Charlie

i2p2www/spec/proposals/159-ssu2.rst

@@ -5,7 +5,7 @@ SSU2
     :author: eyedeekay, orignal, zlatinb, zzz
     :created: 2021-09-12
     :thread: http://zzz.i2p/topics/2612
-    :lastupdated: 2022-07-29
+    :lastupdated: 2022-08-04
     :status: Open
     :target: 0.9.56
 
@@ -5719,9 +5719,9 @@ Signature algorithm: Sign the following data with the Charlie's router signing k
 - nonce: 4 byte nonce
 - timestamp: 4 byte timestamp (seconds)
 - ver: 1 byte SSU version
-- csz: 1 byte endpoint (port + IP) size (6 or 18)
-- CharliePort: 2 byte Charlie's port number
-- Charlie IP: (csz - 2) byte Charlie IP address
+- csz: 1 byte endpoint (port + IP) size (0 or 6 or 18)
+- CharliePort: 2 byte Charlie's port number (not present if csz is 0)
+- Charlie IP: (csz - 2) byte Charlie IP address (not present if csz is 0)
 
 If Bob rejects (response code 1-63),
 Bob signs the response and includes it in this block.