Fix assigning error in SecurityManager

Change-Id: I275aa91b6d1344a62679f528104022f508ee1bd0
Reviewed-on: https://weave-review.googlesource.com/2204
Reviewed-by: Vitaly Buka <vitalybuka@google.com>
diff --git a/src/privet/security_manager.cc b/src/privet/security_manager.cc
index 4cd9276..2a3dc08 100644
--- a/src/privet/security_manager.cc
+++ b/src/privet/security_manager.cc
@@ -185,6 +185,9 @@
   std::vector<uint8_t> auth_decoded;
   if (auth_type != AuthType::kAnonymous &&
       !Base64Decode(auth_code, &auth_decoded)) {
+    Error::AddToPrintf(error, FROM_HERE, errors::kDomain,
+                       errors::kInvalidAuthorization,
+                       "Invalid auth_code encoding: %s", auth_code.c_str());
     return false;
   }