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>

include/libcamera/internal/ipa_proxy.h

@@ -27,6 +27,8 @@ public:
 
 	std::string configurationFile(const std::string &file) const;
 
+	void stop() override = 0;
+
 protected:
 	std::string resolvePath(const std::string &file) const;