utils: ipc: proxy: Process pending messages

Events may be queued to the pipeline handler between the pipeline
handler entering the ::stop() function, and before the call to stop the
IPA has completed.

Handle these events by dispatching all pending messages at the proxy
after the IPA has fully stopped.

Reviewed-by: Jacopo Mondi <jacopo@jmondi.org>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Kieran Bingham <kieran.bingham@ideasonboard.com>

utils/ipc/generators/libcamera_templates/proxy_functions.tmpl

@@ -31,6 +31,8 @@
 	thread_.exit();
 	thread_.wait();
 
+	Thread::current()->dispatchMessages(Message::Type::InvokeMessage);
+
 	running_ = false;
 {%- endmacro -%}