fix bad content length errors when using ranges
fix bad content length errors when using ranges

need to save the expected content length in some dedicated member since
r->headers_out.content_length_n may be manipulated by some nginx filter
(e.g. the range filter) leading to 'actual content length xx is different
than reported length yy' errors

kaltura/nginx-vod-module,kaltura/nginx-vod-module,doublex/nginx-vod-module,doublex/nginx-vod-module,DBezemer/nginx-vod-module,DBezemer/nginx-vod-module,DBezemer/nginx-vod-module,doublex/nginx-vod-module,DBezemer/nginx-vod-module,BlackWizard/nginx-vod-module,DBezemer/nginx-vod-module,BlackWizard/nginx-vod-module,kaltura/nginx-vod-module,doublex/nginx-vod-module,BlackWizard/nginx-vod-module,doublex/nginx-vod-module,BlackWizard/nginx-vod-module,DBezemer/nginx-vod-module,doublex/nginx-vod-module,BlackWizard/nginx-vod-module,kaltura/nginx-vod-module,BlackWizard/nginx-vod-module,kaltura/nginx-vod-module,kaltura/nginx-vod-module