tree: fix tuple encoding performance regression

This commit fixes a performance regression in pgwire encoding of tuples
introduced in #95009.

Informs #98306

Epic: None

Release note: None

pkg/sql/sem/tree/pgwire_encode.go

@@ -44,11 +44,14 @@ func (d *DTuple) pgwireFormat(ctx *FmtCtx) {
 	// string printer called pgwireFormatStringInTuple().
 	ctx.WriteByte('(')
 	comma := ""
+	tc := d.ResolvedType().TupleContents()
 	for i, v := range d.D {
 		ctx.WriteString(comma)
-		t := v.ResolvedType()
-		if tc := d.ResolvedType().TupleContents(); i < len(tc) {
+		var t *types.T
+		if i < len(tc) {
 			t = tc[i]
+		} else {
+			t = v.ResolvedType()
 		}
 		switch dv := UnwrapDatum(nil, v).(type) {
 		case dNull: