Fix wrong error check in schemas.go

The error is assigned to r.err but checked is err, fix this by checking r.err.
Found with nilness analyzer.

Fixes capnproto#147

Also delete unreachable return nil in marshal.go

CONTRIBUTORS

@@ -27,6 +27,7 @@ Jason E. Aten <[email protected]>
 Johan Hernandez <[email protected]>
 Joonsung Lee <[email protected]>
 Lev Radomislensky <[email protected]>
+Lukas Vogel <[email protected]> <[email protected]>
 Martin Sucha <[email protected]>
 Peter Waldschmidt <[email protected]>
 Ross Light <[email protected]> <[email protected]>

encoding/text/marshal.go

@@ -461,7 +461,6 @@ func (enc *Encoder) marshalList(elem schema.Type, l capnp.List) error {
 	default:
 		return fmt.Errorf("unknown list type %v", elem.Which())
 	}
-	return nil
 }
 
 func (enc *Encoder) marshalEnum(typ uint64, val uint16) error {

schemas/schemas.go

@@ -112,7 +112,7 @@ func (r *record) read() ([]byte, error) {
 		}
 		p := packed.NewReader(bufio.NewReader(z))
 		r.data, r.err = ioutil.ReadAll(p)
-		if err != nil {
+		if r.err != nil {
 			r.data = nil
 			return
 		}