Add null check for sync authorities of an account type

This protects against a potential NPE if there are no sync authorities for
an account of a given type.

Bug: 17612697
Change-Id: Ifd34b5b7692cbcc8de78d353eedd284e499f954e

src/com/android/settings/accounts/AuthenticatorHelper.java

@@ -190,10 +190,10 @@ final public class AuthenticatorHelper extends BroadcastReceiver {
                 mEnabledAccountTypes.add(account.type);
             }
         }
+        buildAccountTypeToAuthoritiesMap();
         if (mListeningToAccountUpdates) {
             mListener.onAccountsUpdate(mUserHandle);
         }
-        buildAccountTypeToAuthoritiesMap();
     }
 
     @Override