Fix errcheck warnings (excluding tests)

Fix a few "return value of ... is not checked" warnings.

Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>

message.go

@@ -158,7 +158,9 @@ func DecodeMessageWithFDs(rd io.Reader, fds []int) (msg *Message, err error) {
 	if err != nil {
 		return nil, err
 	}
-	binary.Read(bytes.NewBuffer(b), order, &hlength)
+	if err := binary.Read(bytes.NewBuffer(b), order, &hlength); err != nil {
+		return nil, err
+	}
 	if hlength+length+16 > 1<<27 {
 		return nil, InvalidMessageError("message is too long")
 	}
@@ -265,7 +267,9 @@ func (msg *Message) EncodeToWithFDs(out io.Writer, order binary.ByteOrder) (fds
 		return
 	}
 	enc.align(8)
-	body.WriteTo(&buf)
+	if _, err := body.WriteTo(&buf); err != nil {
+		return nil, err
+	}
 	if buf.Len() > 1<<27 {
 		return nil, InvalidMessageError("message is too long")
 	}

transport_unix.go

@@ -102,8 +102,12 @@ func (t *unixTransport) ReadMessage() (*Message, error) {
 	}
 	// csheader[4:8] -> length of message body, csheader[12:16] -> length of
 	// header fields (without alignment)
-	binary.Read(bytes.NewBuffer(csheader[4:8]), order, &blen)
-	binary.Read(bytes.NewBuffer(csheader[12:]), order, &hlen)
+	if err := binary.Read(bytes.NewBuffer(csheader[4:8]), order, &blen); err != nil {
+		return nil, err
+	}
+	if err := binary.Read(bytes.NewBuffer(csheader[12:]), order, &hlen); err != nil {
+		return nil, err
+	}
 	if hlen%8 != 0 {
 		hlen += 8 - (hlen % 8)
 	}
@@ -120,7 +124,10 @@ func (t *unixTransport) ReadMessage() (*Message, error) {
 	if err != nil {
 		return nil, err
 	}
-	Store(vs, &headers)
+	err = Store(vs, &headers)
+	if err != nil {
+		return nil, err
+	}
 	for _, v := range headers {
 		if v.Field == byte(FieldUnixFDs) {
 			unixfds, _ = v.Variant.value.(uint32)