pg: send RowDescription in response to Describe (statement variant)

According to https://www.postgresql.org/docs/9.1/static/protocol-flow.html

  The Describe message (statement variant) specifies the name of an
  existing prepared statement (or an empty string for the unnamed
  prepared statement). The response is a ParameterDescription message
  describing the parameters needed by the statement, followed by a
  RowDescription message describing the rows that will be returned when
  the statement is eventually executed (or a NoData message if the
  statement will not return rows)

h2/src/main/org/h2/server/pg/PgServerThread.java

@@ -308,7 +308,12 @@ public class PgServerThread implements Runnable {
                 if (p == null) {
                     sendErrorResponse("Prepared not found: " + name);
                 } else {
-                    sendParameterDescription(p);
+                    try {
+                        sendParameterDescription(p.prep.getParameterMetaData(), p.paramType);
+                        sendRowDescription(p.prep.getMetaData());
+                    } catch (Exception e) {
+                        sendErrorResponse(e);
+                    }
                 }
             } else if (type == 'P') {
                 Portal p = portals.get(name);
@@ -636,17 +641,14 @@ public class PgServerThread implements Runnable {
         sendMessage();
     }
 
-    private void sendParameterDescription(Prepared p) throws IOException {
-        try {
-            PreparedStatement prep = p.prep;
-            ParameterMetaData meta = prep.getParameterMetaData();
+    private void sendParameterDescription(ParameterMetaData meta, int[] paramTypes) throws Exception {
         int count = meta.getParameterCount();
         startMessage('t');
         writeShort(count);
         for (int i = 0; i < count; i++) {
             int type;
-                if (p.paramType != null && p.paramType[i] != 0) {
-                    type = p.paramType[i];
+            if (paramTypes != null && paramTypes[i] != 0) {
+                type = paramTypes[i];
             } else {
                 type = PgServer.PG_TYPE_VARCHAR;
             }
@@ -654,9 +656,6 @@ public class PgServerThread implements Runnable {
             writeInt(type);
         }
         sendMessage();
-        } catch (Exception e) {
-            sendErrorResponse(e);
-        }
     }
 
     private void sendNoData() throws IOException {