Ensure sequential parameter collection.

PostgresqlStatement.collectBindingParameters(…) now uses concatMap to collect encoded parameter values instead of flatMap to ensure a consistent parameter ordering.

[resolves #482]

Signed-off-by: Mark Paluch <[email protected]>

Author: mp911de

src/main/java/io/r2dbc/postgresql/PostgresqlStatement.java

@@ -266,7 +266,7 @@ private static void tryNextBinding(Iterator<Binding> iterator, Sinks.Many<Bindin
     private static Mono<List<ByteBuf>> collectBindingParameters(Binding binding) {
 
         return Flux.fromIterable(binding.getParameterValues())
-            .flatMap(f -> {
+            .concatMap(f -> {
                 if (f == EncodedParameter.NULL_VALUE) {
                     return Flux.just(Bind.NULL_VALUE);
                 } else {