Fix bug #307: It's impossible to specify indefinite/no timeout for ZOOM_event. Special timeout value -1 now means indefinite timeout (i.e. no timeout).
Fix bug #307: It's impossible to specify indefinite/no timeout for
ZOOM_event. Special timeout value -1 now means indefinite timeout (i.e.
no timeout).

dcrossleyau/yaz,nla/yaz,nla/yaz,dcrossleyau/yaz,dcrossleyau/yaz,nla/yaz,nla/yaz