fix endless parsing

src/main/kotlin/io/emeraldpay/dshackle/upstream/rpcclient/ResponseParser.kt

@@ -164,19 +164,30 @@ abstract class ResponseParser<T> {
                 break
             }
             val token = parser.nextToken()
-            if (token == JsonToken.START_OBJECT) {
+            when (token) {
+                null -> {
+                    return null
+                }
+                JsonToken.START_OBJECT -> {
                     inited = true
                     count++
                     continue
                 }
-            if (token == JsonToken.END_OBJECT) {
+                JsonToken.END_OBJECT -> {
                     count--
                     continue
                 }
-            if (token == JsonToken.VALUE_NULL) {
+                JsonToken.VALUE_NULL -> {
-                // error is just null
                     return null
                 }
+                JsonToken.VALUE_STRING -> {
+                    if (!inited) {
+                        message = parser.valueAsString
+                        break
+                    }
+                }
+                else -> {}
+            }
             val field = parser.currentName()
             if (field == "code" && token == JsonToken.VALUE_NUMBER_INT) {
                 code = parser.intValue

src/test/groovy/io/emeraldpay/dshackle/upstream/rpcclient/ResponseRpcParserSpec.groovy

@@ -223,4 +223,16 @@ class ResponseRpcParserSpec extends Specification {
         !act.hasResult()
     }
 
+    def "Parse non object error"() {
+        setup:
+        def json = '{"jsonrpc": "2.0", "id": 1, "error": "plain error"}'
+        when:
+        def act = parser.parse(json.getBytes())
+        then:
+        act.error != null
+        act.error.message == "plain error"
+        act.hasError()
+        !act.hasResult()
+    }
+
 }