problem: a Websocket based upstream lacks current height until it loaded through Websocket

solution: load initial block through RPC, then continue with Websocket

src/main/kotlin/io/emeraldpay/dshackle/upstream/ChainUpstreams.kt

@@ -59,10 +59,12 @@ class ChainUpstreams (
             upstream.setLag(0)
             upstream.getHead()
         } else {
-            val newHead = EthereumHeadMerge(upstreams.map { it.getHead() })
-            newHead.start()
-            val lagObserver = HeadLagObserver(newHead, upstreams)
-            lagObserver.start()
+            val newHead = EthereumHeadMerge(upstreams.map { it.getHead().getFlux() }).apply {
+                this.start()
+            }
+            val lagObserver = HeadLagObserver(newHead, upstreams).apply {
+                this.start()
+            }
             this.lagObserver = lagObserver
             newHead
         }