libcamera: request: addBuffer(): Do not destroy fence on failure

Take the unique pointer to the `Fence` object by rvalue reference
so that it is not destroyed if the function returns an error code
and does not take ownership of the unique pointer.

Signed-off-by: Barnabás Pőcze <barnabas.pocze@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Stefan Klug <stefan.klug@ideasonboard.com>

include/libcamera/request.h

@@ -53,7 +53,7 @@ public:
 	ControlList &metadata() { return *metadata_; }
 	const BufferMap &buffers() const { return bufferMap_; }
 	int addBuffer(const Stream *stream, FrameBuffer *buffer,
-		      std::unique_ptr<Fence> fence = nullptr);
+		      std::unique_ptr<Fence> &&fence = {});
 	FrameBuffer *findBuffer(const Stream *stream) const;
 
 	uint32_t sequence() const;