Update async_normal.hpp

If response has
...<chunk>CLRF<hex>CLRF<data>...
We need to skip past chunk-data ending CLRF, otherwise we find it again and on next iteration begin==iter
Merge pull request #248 from frejsoya/0.9-devel

fix chunked client async_normal.hpp
Merge branch '0.9-devel' of github.com:cpp-netlib/cpp-netlib into 0.9-devel