Add a check for wxSocketServer creation to the unit tests.

This should prevent an assert failure which happens if we call Accept() on an
invalid server below and also confirm if the server creation really failed or
not.

tests/streams/socketstream.cpp

@@ -69,6 +69,7 @@ protected:
     virtual void *Entry()
     {
         wxSocketServer srv(LocalAddress(m_port), wxSOCKET_REUSEADDR);
+        CPPUNIT_ASSERT( srv.IsOk() );
 
         // FIXME: this is still not atomic, of course and the main thread could
         //        call Connect() before we have time to Accept() but there is