security: Fixing decoding/encoding certificates. Now the test is fully working

Change-Id: Ieaecba4576d1af3abc68e48baa87e8d4d312b702
diff --git a/src/encoding/oid.cpp b/src/encoding/oid.cpp
index 2db72f7..0fb6697 100644
--- a/src/encoding/oid.cpp
+++ b/src/encoding/oid.cpp
@@ -16,8 +16,19 @@
 
 namespace ndn {
 
+OID::OID(const char *oid)
+{
+  construct(oid);
+}
+
 OID::OID(const string& oid)
 {
+  construct(oid);
+}
+
+void
+OID::construct(const std::string &oid)
+{
   string str = oid + ".";
 
   size_t pos = 0;