Reinitialise JSON converter for each index operation.

This is kind of grasping at straws to fix the mysterious bug where
the index is populated with dodgy data seemingly from two items, but
it seems likely to be a reentrancy issue somewhere. This should prevent
any state in the JsonConverter lingering betwen ops.

modules/portal/app/services/search/AkkaStreamsIndexMediator.scala

@@ -58,7 +58,6 @@ case class AkkaStreamsIndexMediatorHandle(
   private val solrServiceConfig = ServiceConfig("solr", config)
   private val solrBaseUrl: Uri = solrServiceConfig.baseUrl + "/update"
   private val jsonSupport = EntityStreamingSupport.json(Integer.MAX_VALUE)
-  private val jsonConverter = new JsonConverter
   private val mapper = new ObjectMapper
   private val writer = mapper.writer().withDefaultPrettyPrinter()
 
@@ -97,7 +96,7 @@ case class AkkaStreamsIndexMediatorHandle(
     .map(node => ByteString.fromArray(writer.writeValueAsBytes(node)))
     .named("json-node-to-bytes")
 
-  private val jsonNodeToDoc: Flow[JsonNode, JsonNode, akka.NotUsed] = Flow[JsonNode]
+  private def jsonNodeToDoc(jsonConverter: JsonConverter): Flow[JsonNode, JsonNode, akka.NotUsed] = Flow[JsonNode]
     .mapConcat[JsonNode](n => jsonConverter.convert(n).asScala.toVector)
     .named("json-node-to-solr-doc")
 
@@ -138,6 +137,7 @@ case class AkkaStreamsIndexMediatorHandle(
 
     val init = java.time.Instant.now()
     var count = 0
+    val jsonConverter = new JsonConverter
 
     val bytesFlow = Source(setCommonHeaders(requests))
       .map { case (r, uri) =>
@@ -156,7 +156,7 @@ case class AkkaStreamsIndexMediatorHandle(
         Source.future(s).flatMapConcat(n => n)
       }
       .flatMapConcat(n => n) // flatten the streams of JsonNodes into one stream
-      .via(jsonNodeToDoc)
+      .via(jsonNodeToDoc(jsonConverter))
       .map { node =>
         logger.trace(writer.writeValueAsString(node))
         count = count + 1