fix a crash with Cursors on ScreenSelectMaster.

src/ScreenSelectMaster.cpp

@@ -754,10 +754,13 @@ float ScreenSelectMaster::DoMenuStart( PlayerNumber pn )
 		}
 	}
 	if( SHOW_CURSOR )
+	{
+		if(m_sprCursor[pn] != NULL)
 		{
 			m_sprCursor[pn]->PlayCommand( "Choose" );
 			fSecs = max( fSecs, m_sprCursor[pn]->GetTweenTimeLeft() );
 		}
+	}
 
 	return fSecs;
 }