[CBR-454] Correct window size when streaming blocks

When a node syncs with mainnet it maintains a window which controls
how many blocks the peer it syncs with is permitted to have outstanding.
The client incorrectly increased the window which, when the server
manages to send faster than the client was able to write to disk would
lead to a very large memory consumtion until all blocks where written.

lib/src/Pos/Diffusion/Full/Block.hs

@@ -397,11 +397,11 @@ streamBlocks logTrace smM logic streamWindow enqueue nodeId tipHeader checkpoint
         -> Word32
         -> IO ()
     retrieveBlocks bvd blockChan conv window = do
-        window' <- if window < halfStreamWindow
+        window' <- if window <= halfStreamWindow
             then do
-                let w' = streamWindow
+                let w' = window + halfStreamWindow
                 traceWith logTrace (Debug, sformat ("Updating Window: "%int%" to "%int) window w')
-                send conv $ MsgUpdate $ MsgStreamUpdate $ w'
+                send conv $ MsgUpdate $ MsgStreamUpdate halfStreamWindow
                 return (w' - 1)
             else return $ window - 1
         block <- retrieveBlock bvd conv