sql: return type mismatch error in plpgsql function returning composite type

Repro:
```
create type compostype as (x int, y varchar);
create or replace function compos() returns compostype as $$
declare x int := 42;
begin
return x;
end;
$$ language plpgsql;
select * from compos();
```

Stacktrace:
```
ERROR: internal error: runtime error: index out of range [0] with length 0
SQLSTATE: XX000
DETAIL: stack trace:
github.com/cockroachdb/cockroach/pkg/util/errorutil/catch.go:29: ShouldCatch()
github.com/cockroachdb/cockroach/pkg/sql/opt/optbuilder/builder.go:211: func1()
GOROOT/src/runtime/panic.go:914: gopanic()
GOROOT/src/runtime/panic.go:114: goPanicIndex()
github.com/cockroachdb/cockroach/pkg/sql/sem/tree/expr.go:1703: NewTypedColumnAccessExpr()
github.com/cockroachdb/cockroach/pkg/sql/opt/norm/fold_constants_funcs.go:610: FoldColumnAccess()
github.com/cockroachdb/cockroach/bazel-out/darwin-fastbuild/bin/pkg/sql/opt/norm/factory.og.go:20645: ConstructColumnAccess()
github.com/cockroachdb/cockroach/bazel-out/darwin-fastbuild/bin/pkg/sql/opt/norm/factory.og.go:23690: Replace()
github.com/cockroachdb/cockroach/pkg/sql/opt/norm/inline_funcs.go:78: func1()
github.com/cockroachdb/cockroach/pkg/sql/opt/norm/inline_funcs.go:80: inlineConstants()
github.com/cockroachdb/cockroach/pkg/sql/opt/norm/inline_funcs.go:40: InlineProjectionConstants()
github.com/cockroachdb/cockroach/bazel-out/darwin-fastbuild/bin/pkg/sql/opt/norm/factory.og.go:1598: ConstructProject()
github.com/cockroachdb/cockroach/pkg/sql/opt/optbuilder/project.go:62: constructProject()
github.com/cockroachdb/cockroach/pkg/sql/opt/optbuilder/routine.go:379: finishBuildLastStmt()
github.com/cockroachdb/cockroach/pkg/sql/opt/optbuilder/routine.go:304: buildRoutine()
github.com/cockroachdb/cockroach/pkg/sql/opt/optbuilder/routine.go:66: buildUDF()
github.com/cockroachdb/cockroach/pkg/sql/opt/optbuilder/scalar.go:551: buildFunction()
github.com/cockroachdb/cockroach/pkg/sql/opt/optbuilder/scalar.go:332: buildScalar()
github.com/cockroachdb/cockroach/pkg/sql/opt/optbuilder/srfs.go:152: buildZip()
github.com/cockroachdb/cockroach/pkg/sql/opt/optbuilder/select.go:184: buildDataSource()
github.com/cockroachdb/cockroach/pkg/sql/opt/optbuilder/select.go:94: buildDataSource()
github.com/cockroachdb/cockroach/pkg/sql/opt/optbuilder/select.go:1435: buildFromWithLateral()
github.com/cockroachdb/cockroach/pkg/sql/opt/optbuilder/select.go:1359: buildFromTables()
github.com/cockroachdb/cockroach/pkg/sql/opt/optbuilder/select.go:1289: buildFrom()
github.com/cockroachdb/cockroach/pkg/sql/opt/optbuilder/select.go:1205: buildSelectClause()
github.com/cockroachdb/cockroach/pkg/sql/opt/optbuilder/select.go:1141: buildSelectStmtWithoutParens()
github.com/cockroachdb/cockroach/pkg/sql/opt/optbuilder/select.go:1099: func1()
github.com/cockroachdb/cockroach/pkg/sql/opt/optbuilder/with.go:116: processWiths()
github.com/cockroachdb/cockroach/pkg/sql/opt/optbuilder/select.go:1098: buildSelect()
github.com/cockroachdb/cockroach/pkg/sql/opt/optbuilder/builder.go:341: buildStmt()
github.com/cockroachdb/cockroach/pkg/sql/opt/optbuilder/builder.go:285: buildStmtAtRootWithScope()
github.com/cockroachdb/cockroach/pkg/sql/opt/optbuilder/builder.go:266: buildStmtAtRoot()

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```

postgres returns the following error:
```
ERROR: cannot return non-composite value from function returning composite type
CONTEXT: PL/pgSQL function compos() line 4 at RETURN
```

Found in pg_regress plpgsql

Jira issue: CRDB-33718