vom: move magicbyte handling into encode/decode.

  * move magicbyte handling into encode/decode and change
   New{Encoder,Decoder} API to no return error any more.

MultiPart: 2/3
Change-Id: I9ceef311128c4b422494d4cd7929bfc1e420508f
diff --git a/lib/security/storage.go b/lib/security/storage.go
index 1690c91..07058f3 100644
--- a/lib/security/storage.go
+++ b/lib/security/storage.go
@@ -25,11 +25,7 @@
 	if err != nil {
 		return err
 	}
-	enc, err := vom.NewEncoder(swc)
-	if err != nil {
-		swc.Close()
-		return err
-	}
+	enc := vom.NewEncoder(swc)
 	if err := enc.Encode(obj); err != nil {
 		swc.Close()
 		return err
@@ -47,9 +43,6 @@
 	if err != nil {
 		return err
 	}
-	dec, err := vom.NewDecoder(vr)
-	if err != nil {
-		return err
-	}
+	dec := vom.NewDecoder(vr)
 	return dec.Decode(obj)
 }