fixup! proto/msgpack: Fix encoding INVALID_{TID,OID}

This is the decoding part of 37dd83e9

go/neo/proto/protogen.go

@@ -1095,13 +1095,18 @@ func (d *decoderM) expectEnum(assignto string, enumType int) {
 }
 
 func (d *decoderM) genBasic(assignto string, typ *types.Basic, userType types.Type) {
-	// zodb.Tid and zodb.Oid are encoded as [8]bin
+	// zodb.Tid and zodb.Oid are encoded as [8]bin or Nil
 	if userType == zodbTid || userType == zodbOid {
+		d.emit("if data[%v] == byte(msgpack.Nil) {", d.n)
+		d.emit("%s = %s(%v)", assignto, typeName(userType), INVALID_ID)
+		d.emit("data = data[%v:]", d.n + 1)
+		d.emit("} else {")
 		d.expectBin8Fix(assignto, 8)
 		d.emit("%s= %s(binary.BigEndian.Uint64(data[%v:]))", assignto, typeName(userType), d.n)
 		d.n += 8
 		d.overflow.Add(8)
-
+		d.resetPos()
+		d.emit("}")
 		return
 	}