Fix stupid bug AGAIN

I missed a bang!

Author: fge

src/main/java/com/github/fge/jsonschema/process/Index.java

@@ -137,7 +137,7 @@ private static JsonNode readOne(final String input)
             final JsonParser parser = MAPPER.getFactory().createParser(reader);
         ) {
             iterator = MAPPER.readValues(parser, JsonNode.class);
-            if (iterator.hasNextValue())
+            if (!iterator.hasNextValue())
                 throw new JsonParseException("no data",
                     new JsonLocation(reader, 0L, 1, 1));
             ret = iterator.nextValue();