fundingmanager: send error directly in CancelPeerReservations

The error channel should never be nil, and it should always be buffered.
Because of this we can send directly on the channel.

fundingmanager.go

@@ -775,13 +775,7 @@ func (f *fundingManager) CancelPeerReservations(nodePub [33]byte) {
 				"node=%x: %v", nodePub[:], err)
 		}
 
-		if resCtx.err != nil {
+		resCtx.err <- fmt.Errorf("peer disconnected")
-			select {
-			case resCtx.err <- fmt.Errorf("peer disconnected"):
-			default:
-			}
-		}
-
 		delete(nodeReservations, pendingID)
 	}