Fix to receive peer requests from just connected nodes

All `self.header_downloaders.keys()` are in `connected_nodes`, and
`self.header_downloaders` keep tracks of nodes which have sent at least
one peer status out of connected nodes.
The following commit will prohibit the node sending peer requests before
it finishes to snapshot sync, so it can send peer requests before share
peer status.
So this changes make the node accept requests from the node who didn't
send any peer status.

Author: foriequal0

sync/src/block/extension.rs

@@ -622,7 +622,7 @@ impl Extension {
     }
 
     fn on_peer_request(&self, from: &NodeId, id: u64, request: RequestMessage) {
-        if !self.header_downloaders.contains_key(from) {
+        if !self.connected_nodes.contains(from) {
             cinfo!(SYNC, "Request from invalid peer #{} received", from);
             return
         }