hyperlink: Factor out str->window in set_hyperlink_stream()
hyperlink: Factor out str->window in set_hyperlink_stream()

The code becomes a bit cleaner when we assign str->window to a temporary
winid_t variable.

wmvanvliet/Chimara,wmvanvliet/Chimara,wmvanvliet/Chimara,wmvanvliet/Chimara,wmvanvliet/Chimara