Update signing to deal with NULL keystore

src/script/sign.cpp

@@ -245,7 +245,7 @@ static bool SignStepCC(const BaseSignatureCreator& creator, const CScript& scrip
                 // first of priv key in our key store or contract address is what we sign with
                 for (auto pk : p.vKeys)
                 {
-                    if (creator.KeyStore().GetKey(pk.GetID(), privKey) && privKey.IsValid())
+                    if (creator.IsKeystoreValid() && creator.KeyStore().GetKey(pk.GetID(), privKey) && privKey.IsValid())
                         break;
 
                     if (pk == CPubKey(ParseHex(C.CChexstr)))

src/script/sign.h

@@ -23,7 +23,8 @@ protected:
 
 public:
     BaseSignatureCreator(const CKeyStore* keystoreIn) : keystore(keystoreIn) {}
-    const CKeyStore& KeyStore() const { return *keystore; };
+    const bool IsKeystoreValid() const { return keystore != NULL; }
+    const CKeyStore& KeyStore() const { return *keystore; }
     virtual ~BaseSignatureCreator() {}
     virtual const BaseSignatureChecker& Checker() const =0;