Fix missed cases in libpq's error handling.

Commit 618c167 invented an "error_result" flag in PGconn, which
intends to represent the state that we have an error condition and
need to build a PGRES_FATAL_ERROR PGresult from the message text in
conn->errorMessage, but have not yet done so.  (Postponing construction
of the error object simplifies dealing with out-of-memory conditions
and with concatenation of messages for multiple errors.)  For nearly all
purposes, this "virtual" PGresult object should act the same as if it
were already materialized.  But a couple of places in fe-protocol3.c
didn't get that memo, and were only testing conn->result as they used
to, without also checking conn->error_result.

In hopes of reducing the probability of similar mistakes in future,
I invented a pgHavePendingResult() macro that includes both tests.

Per report from Peter Eisentraut.

Discussion: https://postgr.es/m/b52277b9-fa66-b027-4a37-fb8989c73ff8@enterprisedb.com

Author: tglsfdc

src/interfaces/libpq/fe-exec.c

@@ -1196,6 +1196,7 @@ pqSaveParameterStatus(PGconn *conn, const char *name, const char *value)
  *	  Returns 1 if OK, 0 if error occurred.
  *
  * On error, *errmsgp can be set to an error string to be returned.
+ * (Such a string should already be translated via libpq_gettext().)
  * If it is left NULL, the error is presumed to be "out of memory".
  *
  * In single-row mode, we create a new result holding just the current row,
@@ -1986,7 +1987,7 @@ PQsetSingleRowMode(PGconn *conn)
 		(conn->cmd_queue_head->queryclass != PGQUERY_SIMPLE &&
 		 conn->cmd_queue_head->queryclass != PGQUERY_EXTENDED))
 		return 0;
-	if (conn->result || conn->error_result)
+	if (pgHavePendingResult(conn))
 		return 0;
 
 	/* OK, set flag */
@@ -2941,7 +2942,7 @@ PQfn(PGconn *conn,
 	}
 
 	if (conn->sock == PGINVALID_SOCKET || conn->asyncStatus != PGASYNC_IDLE ||
-		conn->result || conn->error_result)
+		pgHavePendingResult(conn))
 	{
 		appendPQExpBufferStr(&conn->errorMessage,
 							 libpq_gettext("connection in wrong state\n"));

src/interfaces/libpq/fe-protocol3.c

@@ -209,7 +209,7 @@ pqParseInput3(PGconn *conn)
 				case 'C':		/* command complete */
 					if (pqGets(&conn->workBuffer, conn))
 						return;
-					if (conn->result == NULL)
+					if (!pgHavePendingResult(conn))
 					{
 						conn->result = PQmakeEmptyPGresult(conn,
 														   PGRES_COMMAND_OK);
@@ -263,7 +263,7 @@ pqParseInput3(PGconn *conn)
 					}
 					break;
 				case 'I':		/* empty query */
-					if (conn->result == NULL)
+					if (!pgHavePendingResult(conn))
 					{
 						conn->result = PQmakeEmptyPGresult(conn,
 														   PGRES_EMPTY_QUERY);
@@ -281,7 +281,7 @@ pqParseInput3(PGconn *conn)
 					if (conn->cmd_queue_head &&
 						conn->cmd_queue_head->queryclass == PGQUERY_PREPARE)
 					{
-						if (conn->result == NULL)
+						if (!pgHavePendingResult(conn))
 						{
 							conn->result = PQmakeEmptyPGresult(conn,
 															   PGRES_COMMAND_OK);
@@ -362,7 +362,7 @@ pqParseInput3(PGconn *conn)
 					if (conn->cmd_queue_head &&
 						conn->cmd_queue_head->queryclass == PGQUERY_DESCRIBE)
 					{
-						if (conn->result == NULL)
+						if (!pgHavePendingResult(conn))
 						{
 							conn->result = PQmakeEmptyPGresult(conn,
 															   PGRES_COMMAND_OK);
@@ -2133,7 +2133,7 @@ pqFunctionCall3(PGconn *conn, Oid fnid,
 				 * report COMMAND_OK.  Otherwise, the backend violated the
 				 * protocol, so complain.
 				 */
-				if (!(conn->result || conn->error_result))
+				if (!pgHavePendingResult(conn))
 				{
 					if (status == PGRES_COMMAND_OK)
 					{

src/interfaces/libpq/libpq-int.h

@@ -852,6 +852,14 @@ extern void pqTraceOutputNoTypeByteMessage(PGconn *conn, const char *message);
 	(resetPQExpBuffer(&(conn)->errorMessage), \
 	 (conn)->errorReported = 0)
 
+/*
+ * Check whether we have a PGresult pending to be returned --- either a
+ * constructed one in conn->result, or a "virtual" error result that we
+ * don't intend to materialize until the end of the query cycle.
+ */
+#define pgHavePendingResult(conn) \
+	((conn)->result != NULL || (conn)->error_result)
+
 /*
  * this is so that we can check if a connection is non-blocking internally
  * without the overhead of a function call