Fix some possible writev handling bugs in EventedServer.
Fix some possible writev handling bugs in EventedServer.

kewaunited/passenger,openSUSE/passenger,cgvarela/passenger,clemensg/passenger,fabiokung/passenger-debian,phusion/passenger,kewaunited/passenger,bf4/passenger,kewaunited/passenger,bf4/passenger,antek-drzewiecki/passenger,antek-drzewiecki/passenger,jawj/passenger,jawj/passenger,gravitystorm/passenger,clemensg/passenger,pkmiec/passenger,clemensg/passenger,clemensg/passenger,antek-drzewiecki/passenger,erikogan/passenger,kewaunited/passenger,erikogan/passenger,antek-drzewiecki/passenger,antek-drzewiecki/passenger,cgvarela/passenger,antek-drzewiecki/passenger,fabiokung/passenger-debian,fabiokung/passenger-debian,phusion/passenger,pkmiec/passenger,kewaunited/passenger,openSUSE/passenger,phusion/passenger,gravitystorm/passenger,bf4/passenger,phusion/passenger,pkmiec/passenger,jawj/passenger,antek-drzewiecki/passenger,bf4/passenger,cgvarela/passenger,bf4/passenger,openSUSE/passenger,erikogan/passenger,erikogan/passenger,gravitystorm/passenger,phusion/passenger,phusion/passenger,jawj/passenger,bf4/passenger,antek-drzewiecki/passenger,cgvarela/passenger,jawj/passenger,kewaunited/passenger,clemensg/passenger,gravitystorm/passenger,gravitystorm/passenger,gravitystorm/passenger,kewaunited/passenger,phusion/passenger,phusion/passenger,pkmiec/passenger,clemensg/passenger,pkmiec/passenger,bf4/passenger,cgvarela/passenger,openSUSE/passenger,fabiokung/passenger-debian,clemensg/passenger,kewaunited/passenger,jawj/passenger,clemensg/passenger,openSUSE/passenger,pkmiec/passenger,erikogan/passenger,pkmiec/passenger,jawj/passenger,fabiokung/passenger-debian,openSUSE/passenger,cgvarela/passenger,cgvarela/passenger,fabiokung/passenger-debian,erikogan/passenger,cgvarela/passenger