fix non-stats query

Author: jan-elastic

x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/approximate/Approximate.java

@@ -386,7 +386,7 @@ public void onResponse(Result result) {
                             cluster -> cluster.getFailures().stream().anyMatch(e -> e.getCause() instanceof UnsupportedOperationException)
                         );
                 if (esStatsQueryExecuted) {
-                    logger.debug("not approximating stats query");
+                    logger.debug("stats query succeeded; returning exact result");
                     listener.onResponse(result);
                 } else {
                     result.pages().forEach(Page::close);
@@ -396,9 +396,10 @@ public void onResponse(Result result) {
 
             @Override
             public void onFailure(Exception e) {
-                if (e instanceof UnsupportedOperationException) {
+                if (e.getCause() instanceof UnsupportedOperationException) {
                     runner.run(toPhysicalPlan.apply(sourceCountPlan()), configuration, foldContext, sourceCountListener(listener));
                 } else {
+                    logger.debug("stats query failed; returning error");
                     listener.onFailure(e);
                 }
             }