coverity#1437958 Uninitialized pointer field

Change-Id: I569c4367cc968f968c0f864bb3e231a7417d7560
Reviewed-on: https://gerrit.libreoffice.org/57454Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>

oox/source/crypto/CryptTools.cxx

@@ -134,6 +134,7 @@ struct CryptoImpl
         : mContext(nullptr)
         , mSecParam(nullptr)
         , mSymKey(nullptr)
+        , mpSlot(nullptr)
     {
         // Initialize NSS, database functions are not needed
         NSS_NoDB_Init(nullptr);