Fix ginint4_queryextract() to actually do what it was intended to do for an

unsatisfiable query, such as indexcol && empty_array.  It should return -1
to tell GIN no scan is required; but silly typo disabled the logic for that,
resulting in unnecessary "GIN indexes do not support whole-index scans" error.
Per bug report from Jeff Trout.

Back-patch to 8.3 where the logic was introduced.

contrib/intarray/_int_gin.c

 /*
- * $PostgreSQL: pgsql/contrib/intarray/_int_gin.c,v 1.10 2009/06/11 14:48:51 momjian Exp $
+ * $PostgreSQL: pgsql/contrib/intarray/_int_gin.c,v 1.11 2010/03/25 15:50:10 tgl Exp $
  */
 #include "postgres.h"
 
@@ -65,7 +65,7 @@ ginint4_queryextract(PG_FUNCTION_ARGS)
 		}
 	}
 
-	if (nentries == 0)
+	if (*nentries == 0)
 	{
 		switch (strategy)
 		{