The storage element may be empty on fetch fail
The storage element may be empty on fetch fail

A failed fetch won't have the storage trimmed, which may result in an
empty storage element in the body list. Do not assert on non-empty
size in the simple iterator.

Fixes: #2186

gquintard/Varnish-Cache,gquintard/Varnish-Cache,feld/Varnish-Cache,gquintard/Varnish-Cache,feld/Varnish-Cache,feld/Varnish-Cache,feld/Varnish-Cache,feld/Varnish-Cache,gquintard/Varnish-Cache