Fix uninitialized memory reference.

Without this, when partdesc->nparts == 0, we end up calling
ExecBuildSlotPartitionKeyDescription without initializing values
and isnull.

Reported by Coverity via Michael Paquier.  Patch by Michael Paquier,
reviewed and revised by Amit Langote.

Discussion: http://postgr.es/m/CAB7nPqQ3mwkdMoPY-ocgTpPnjd8TKOadMxdTtMLvEzF8480Zfg@mail.gmail.com

src/backend/executor/execPartition.c

@@ -206,13 +206,6 @@ ExecFindPartition(ResultRelInfo *resultRelInfo, PartitionDispatch *pd,
 			slot = myslot;
 		}
 
-		/* Quick exit */
-		if (partdesc->nparts == 0)
-		{
-			result = -1;
-			break;
-		}
-
 		/*
 		 * Extract partition key from tuple. Expression evaluation machinery
 		 * that FormPartitionKeyDatum() invokes expects ecxt_scantuple to
@@ -223,6 +216,17 @@ ExecFindPartition(ResultRelInfo *resultRelInfo, PartitionDispatch *pd,
 		 */
 		ecxt->ecxt_scantuple = slot;
 		FormPartitionKeyDatum(parent, slot, estate, values, isnull);
+
+		/*
+		 * Nothing for get_partition_for_tuple() to do if there are no
+		 * partitions to begin with.
+		 */
+		if (partdesc->nparts == 0)
+		{
+			result = -1;
+			break;
+		}
+
 		cur_index = get_partition_for_tuple(rel, values, isnull);
 
 		/*

src/test/regress/expected/insert.out

@@ -165,6 +165,10 @@ create table range_parted (
 	a text,
 	b int
 ) partition by range (a, (b+0));
+-- no partitions, so fail
+insert into range_parted values ('a', 11);
+ERROR:  no partition of relation "range_parted" found for row
+DETAIL:  Partition key of the failing row contains (a, (b + 0)) = (a, 11).
 create table part1 partition of range_parted for values from ('a', 1) to ('a', 10);
 create table part2 partition of range_parted for values from ('a', 10) to ('a', 20);
 create table part3 partition of range_parted for values from ('b', 1) to ('b', 10);

src/test/regress/sql/insert.sql

@@ -90,6 +90,10 @@ create table range_parted (
 	a text,
 	b int
 ) partition by range (a, (b+0));
+
+-- no partitions, so fail
+insert into range_parted values ('a', 11);
+
 create table part1 partition of range_parted for values from ('a', 1) to ('a', 10);
 create table part2 partition of range_parted for values from ('a', 10) to ('a', 20);
 create table part3 partition of range_parted for values from ('b', 1) to ('b', 10);