Closes #2207. Thanks to Abilio Marques.

Coverity scan #1451483.

This could occur when a message publication is attempted when the broker
is temporarily unavailable.

Closes #2187. Thanks to JsBergbau.

Coverity #1450782.

Closes #2190. Thanks to RengeRenge.

This older Microsoft compiler does not support mixing declarations and
code and misses some error defines. This commit enables building with
VS2008 by moving up some variable declarations and defining error
codes to their WinSock counterparts in case they're not defined.

Signed-off-by: Christian Beier <info@christianbeier.net>

Happens if `per_listener_settings true` is set, and a SIGHUP is sent to
the broker before a client has reconnected to the broker.

Closes #2167. Thanks to momoskitto.

If sending mosquitto_sub output to a pipe, mosquitto_sub will now detect
that the pipe has closed and disconnect.

Closes #2164. Thanks to Frantisek Fuka.

CMake: Fix undefined symbols in plugins

Closes #2089. Thanks to YerayAlonso.

Closes #2098.

Closes #2136. Thanks to chuckunix.

CVE-xxxx-xxxx: If an authenticated client connected with MQTT v5 sent a
malformed CONNACK message to the broker a NULL pointer dereference occurred,
most likely resulting in a segfault. This will be updated with the CVE
number when it is assigned.
Affects versions 2.0.0 to 2.0.9 inclusive.

Closes #2163. Thanks to Bryan Pearson.

This would occur if a client was using `mosquitto_loop_start()`, then if
the connection failed due to the remote server being inaccessible they
called `mosquitto_loop_stop(, true)` and recreated the mosquitto object.

See: https://www.eclipse.org/forums/index.php?t=rview&goto=1839865#msg_1839865

Closes #2160. Thanks to Ozaq.

Closes #2152. Thanks to jetpax.