[core] handle ENOSPC with pwritev() (#3171)
[core] handle ENOSPC with pwritev() (#3171)

handle ENOSPC with pwritev() and fallback to next item in
server.upload-dirs list

x-ref:
  "File upload regression with --disable-lfs"
  https://redmine.lighttpd.net/issues/3171

gstrauss/lighttpd1.4,lighttpd/lighttpd1.4,lighttpd/lighttpd1.4,lighttpd/lighttpd1.4,gstrauss/lighttpd1.4,gstrauss/lighttpd1.4,lighttpd/lighttpd1.4,gstrauss/lighttpd1.4,lighttpd/lighttpd1.4,gstrauss/lighttpd1.4,lighttpd/lighttpd1.4,gstrauss/lighttpd1.4