Fixed explain error handling

mysql-test/r/subselect.result:
  test of subselect explain
mysql-test/t/subselect.test:
  test of subselect explain

mysql-test/r/subselect.result

@@ -279,6 +279,8 @@ UNIQUE KEY `numreponse` (`numreponse`),
 KEY `pseudo` (`pseudo`,`numeropost`)
 ) TYPE=MyISAM;
 INSERT INTO threadhardwarefr7 (numeropost,numreponse,pseudo) VALUES (1,1,'joce'),(1,2,'joce'),(1,3,'test');
+EXPLAIN SELECT numreponse FROM threadhardwarefr7 WHERE numeropost='1' AND numreponse=(SELECT 1 FROM threadhardwarefr7 WHERE numeropost='1');
+Subselect returns more than 1 record
 EXPLAIN SELECT MAX(numreponse) FROM threadhardwarefr7 WHERE numeropost='1';
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	SIMPLE								Select tables optimized away

mysql-test/t/subselect.test

@@ -177,7 +177,8 @@ CREATE TABLE `threadhardwarefr7` (
   KEY `pseudo` (`pseudo`,`numeropost`)
 ) TYPE=MyISAM;
 INSERT INTO threadhardwarefr7 (numeropost,numreponse,pseudo) VALUES (1,1,'joce'),(1,2,'joce'),(1,3,'test');
-
+-- error 1240
+EXPLAIN SELECT numreponse FROM threadhardwarefr7 WHERE numeropost='1' AND numreponse=(SELECT 1 FROM threadhardwarefr7 WHERE numeropost='1');
 EXPLAIN SELECT MAX(numreponse) FROM threadhardwarefr7 WHERE numeropost='1';
 EXPLAIN SELECT numreponse FROM threadhardwarefr7 WHERE numeropost='1' AND numreponse=(SELECT MAX(numreponse) FROM threadhardwarefr7 WHERE numeropost='1');
 drop table if exists threadhardwarefrtest7;

sql/sql_select.cc

@@ -371,13 +371,17 @@ JOIN::optimize()
   }
 #endif
 
-  conds=optimize_cond(conds,&cond_value);
-  if (thd->fatal_error || thd->net.report_error)
+  conds= optimize_cond(conds,&cond_value);
+  if (thd->fatal_error)
   {
+    // quick abort
     delete procedure;
-    error = 0;
+    error= 0;
     DBUG_RETURN(1);
-  }
+  } else if (thd->net.report_error)
+    // normal error processing & cleanup
+    DBUG_RETURN(-1);
+
   if (cond_value == Item::COND_FALSE || !unit->select_limit_cnt)
   {					/* Impossible cond */
     zero_result_cause= "Impossible WHERE";
@@ -7516,8 +7520,8 @@ int mysql_explain_union(THD *thd, SELECT_LEX_UNIT *unit, select_result *result)
       break;
 
   }
-  if (res > 0)
-    res= -res; // mysql_explain_select do not report error
+  if (res > 0 || thd->net.report_error)
+    res= -1; // mysql_explain_select do not report error
   DBUG_RETURN(res);
 }