SlingboxLib: Fix alternative CSlingbox constructor

```C++
CSlingbox::CSlingbox(const char * szAddress, unsigned int uiPort /* = 5001 */) {
  // Call default constructor
  CSlingbox();
  ...
}
```
"CSlingbox();" - object is created and immediately removed.
Therefore with CSlingbox(const char * szAddress, unsigned int uiPort /* = 5001 */) class members will not be initialized.

I sended this patch here because slingboxlib repo is dead.