SlingboxLib: Fix alternative CSlingbox constructor

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.
Merge pull request #5282 from maksqwe/slingboxlib_fix

SlingboxLib: Fix alternative CSlingbox constructor