Patch against cpp-netlib-0.12.0 to fix empty body bug in HTTP POST

See https://github.com/cpp-netlib/cpp-netlib/pull/637

patches/cpp-netlib-0.12.0-final.patch

+diff -ur cpp-netlib-0.12.0-final/boost/network/protocol/http/server/async_connection.hpp cpp-netlib-0.12.0-final.patched/boost/network/protocol/http/server/async_connection.hpp
+--- cpp-netlib-0.12.0-final/boost/network/protocol/http/server/async_connection.hpp	2016-03-30 13:38:49.000000000 +0200
++++ cpp-netlib-0.12.0-final.patched/boost/network/protocol/http/server/async_connection.hpp	2018-09-05 09:35:15.000000000 +0200
+@@ -378,7 +378,7 @@
+       boost::throw_exception(std::system_error(*error_encountered));
+     if (new_start != read_buffer_.begin()) {
+       input_range input =
+-          boost::make_iterator_range(new_start, read_buffer_.end());
++          boost::make_iterator_range(new_start, data_end);
+       buffer_type::iterator start_tmp = new_start;
+       new_start = read_buffer_.begin();
+       auto self = this->shared_from_this();
+@@ -389,11 +389,12 @@
+     }
+ 
+     auto self = this->shared_from_this();
+-    socket().async_read_some(asio::buffer(read_buffer_),
+-                             strand.wrap([this, self, callback](
+-                                 std::error_code ec, size_t bytes_transferred) {
+-                               callback(ec, bytes_transferred);
+-                             }));
++    socket().async_read_some(
++        asio::buffer(read_buffer_),
++        strand.wrap([this, self, callback](std::error_code ec,
++                                           size_t bytes_transferred) {
++          this->wrap_read_handler(callback, ec, bytes_transferred);
++        }));
+   }
+ 
+   /// Returns a reference to the underlying socket.