In case empty selector in SubscribeNative we should use default dynamic merged head. (#172)

src/main/kotlin/io/emeraldpay/dshackle/upstream/ethereum_pos/EthereumPosMultiStream.kt

@@ -158,6 +158,9 @@ open class EthereumPosMultiStream(
     }
 
     override fun getHead(mather: Selector.Matcher): Head =
+        if (mather == Selector.empty) {
+            head
+        } else {
             filteredHeads.computeIfAbsent(mather.describeInternal().intern()) { _ ->
                 upstreams.filter { mather.matches(it) }
                     .apply {
@@ -168,12 +171,17 @@ open class EthereumPosMultiStream(
                         when (it.size) {
                             0 -> EmptyHead()
                             1 -> selected.first()
-                        else -> MergedHead(selected, PriorityForkChoice(), "ETH head for ${it.map { it.getId() }}").apply {
+                            else -> MergedHead(
+                                selected,
+                                PriorityForkChoice(),
+                                "ETH head for ${it.map { it.getId() }}"
+                            ).apply {
                                 start()
                             }
                         }
                     }
             }
+        }
 
     override fun getFeeEstimation(): ChainFees {
         return feeEstimation