Try to fix multiple head subscriptions (erigontech#1565)

Co-authored-by: Alexey Sharp <[email protected]>

ethdb/remote/remotedbserver/events.go

@@ -30,7 +30,7 @@ func (e *Events) OnNewHeader(newHeader *types.Header) {
 			// remove subscription
 			if i == len(e.headerSubscriptions)-1 {
 				e.headerSubscriptions = e.headerSubscriptions[:i]
-			} else {
+			} else if i < len(e.headerSubscriptions)-1 {
 				e.headerSubscriptions = append(e.headerSubscriptions[:i], e.headerSubscriptions[i+1:]...)
 			}
 		}