Conditions of the form IN(SELECT ...) where slow and increased the database size…

Conditions of the form IN(SELECT ...) where slow and increased the database size if the subquery result size was larger then the configured MAX_MEMORY_ROWS.

h2/src/main/org/h2/result/ResultTempTable.java

@@ -78,7 +78,10 @@ public class ResultTempTable implements ResultExternal {
     }
 
     public synchronized ResultExternal createShallowCopy() {
-        if (closed || parent != null) {
+        if (parent != null) {
+            return parent.createShallowCopy();
+        }
+        if (closed) {
             return null;
         }
         childCount++;