Handler::Proxy raise error with POST request without content-length
Bug found by Pascal PEJAC.
{panel:title=error.log} The LENGTH argument can't be negative at /usr/lib/perl5/vendor_perl/5.8.8/Lemonldap/NG/Handler/Proxy.pm line 90. {panel}
We must test content-length before reading the socket. If no length, the read function should not be called.