Add an opr_sanity check for misdefined aggregates that have transition

type different from input type but are expecting ExecAgg to insert the
first non-null input as the starting transition value.  This has always
been verboten, but wasn't checked for until now...

src/test/regress/expected/opr_sanity.out

@@ -479,6 +479,17 @@ WHERE p1.aggfinalfn = p2.oid AND
 -----+---------+-----+---------
 (0 rows)
 
+-- If transfn is strict then either initval should be non-NULL, or
+-- basetype should equal transtype so that the first non-null input
+-- can be assigned as the state value.
+SELECT p1.oid, p1.aggname, p2.oid, p2.proname
+FROM pg_aggregate AS p1, pg_proc AS p2
+WHERE p1.aggtransfn = p2.oid AND p2.proisstrict AND
+    p1.agginitval IS NULL AND p1.aggbasetype != p1.aggtranstype;
+ oid | aggname | oid | proname 
+-----+---------+-----+---------
+(0 rows)
+
 -- **************** pg_opclass ****************
 -- There should not be multiple entries in pg_opclass with the same
 -- nonzero opcdeftype value, because there can be only one default opclass

src/test/regress/sql/opr_sanity.sql

@@ -400,6 +400,15 @@ WHERE p1.aggfinalfn = p2.oid AND
      p2.pronargs != 1 OR
      p1.aggtranstype != p2.proargtypes[0]);
 
+-- If transfn is strict then either initval should be non-NULL, or
+-- basetype should equal transtype so that the first non-null input
+-- can be assigned as the state value.
+
+SELECT p1.oid, p1.aggname, p2.oid, p2.proname
+FROM pg_aggregate AS p1, pg_proc AS p2
+WHERE p1.aggtransfn = p2.oid AND p2.proisstrict AND
+    p1.agginitval IS NULL AND p1.aggbasetype != p1.aggtranstype;
+
 -- **************** pg_opclass ****************
 
 -- There should not be multiple entries in pg_opclass with the same