libcamera: ipa_proxy: Allow stop() on a stopped IPA

To make error handling easier in callers, allow the stop() function to
be called when the proxy is already stopped, or not started yet.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Jacopo Mondi <jacopo@jmondi.org>
Reviewed-by: Niklas Söderlund <niklas.soderlund@ragnatech.se>

src/libcamera/proxy/ipa_proxy_thread.cpp

@@ -121,6 +121,9 @@ int IPAProxyThread::start()
 
 void IPAProxyThread::stop()
 {
+	if (!running_)
+		return;
+
 	running_ = false;
 
 	proxy_.invokeMethod(&ThreadProxy::stop, ConnectionTypeBlocking);