util.dbuffer: Add efficient shortcuts for discard() in certain cases
If the buffer is already empty, nothing to do. If we're throwing away the
whole buffer, we can just empty it and avoid read_chunk() (which in turn
may collapse()). These shortcuts are much more efficient.
# Prosody IM Server
## Description
Prosody is a server for Jabber/XMPP written in Lua. It aims to be easy to use
and light on resources. For developers, it aims to give a flexible system on
which to rapidly develop added functionality or rapidly prototype new
protocols.
## Useful links
Homepage: https://prosody.im/
Download: https://prosody.im/download
Documentation: https://prosody.im/doc/
Issue tracker: https://issues.prosody.im/
Jabber/XMPP Chat:
Address:
prosody@conference.prosody.im
Web interface:
https://chat.prosody.im/
Mailing lists:
User support and discussion:
https://groups.google.com/group/prosody-users
Development discussion:
https://groups.google.com/group/prosody-dev
## Installation
See the accompanying INSTALL file for help on building Prosody from source.
Alternatively see our guide at https://prosody.im/doc/install