[CONJ-616] avoiding NPE on connection when using master slave configu…

…ration and no host found

src/main/java/org/mariadb/jdbc/internal/failover/impl/MastersSlavesListener.java

@@ -220,6 +220,7 @@ public Object invoke(Method method, Object[] args) throws Throwable {
     @Override
     public boolean versionGreaterOrEqual(int major, int minor, int patch) {
         Protocol protocol = (currentProtocol != null) ? currentProtocol : secondaryProtocol;
+        if (protocol == null) return false;
         return protocol.versionGreaterOrEqual(major, minor, patch);
     }