Deal with absent or incorrect ?chunk value

Pass blockSize to node.store only when correct REST ?chunk value was provided, otherwise node.store will use  its default value.

Also added MaxBlockSize=1 GB, so we have reasonable limit to block sizes provided by users.

codex/rest/api.nim

@@ -181,7 +181,7 @@ proc initRestApi*(node: CodexNodeRef, conf: CodexConf): RestRouter =
 
       try:
         let runUpload =
-          if blockSize =? chunk.get:
+          if (chunkOpt =? chunk) and (blockSize =? chunkOpt) and (blockSize <= MaxBlockSize):
             node.store(bodyStream, blockSize = blockSize.int)
           else:
             node.store(bodyStream)