Added assertions and enforcements to ZlibInputStream and made sure that flush() is not called more than once.
Added assertions and enforcements to ZlibInputStream and made sure that flush() is not called more than once.

AndreyMZ/vibe.d,chalucha/vibe.d,yannick/vibe.d,1100110/vibe.d,mfrischknecht/vibe.d,nathanchristenson/vibe.d,DBankov/vibe.d,gedaiu/vibe.d,etcimon/vibe.0,alphaKAI/vibe.d,etcimon/vibe.d,alphaKAI/vibe.d,etcimon/vibe.0,Yoplitein/vibe.d,alphaKAI/vibe.d,dkillebrew/vibe.d,sigod/vibe.d,sigod/vibe.d,nathanchristenson/vibe.d,Yoplitein/vibe.d,jkm/vibe.d,machindertechnologies/vibe.d,veelo/vibe.d,jkm/vibe.d,redstar/vibe.d,Yoplitein/vibe.d,Mihail-K/vibe.d,brianloveJesus/vibe.d,ColdenCullen/vibe.d,nathanchristenson/vibe.d,sigod/vibe.d,cybevnm/vibe.d,rejectedsoftware/vibe.d,Geod24/vibe.d,etcimon/vibe.d,schuetzm/vibe.d,fast4shoot/vibe.d,Kozzi11/vibe.d