libcamera: pipeline_handler: Fatal if registering camera without media devices

Pipeline handlers must acquire media devices via
PipelineHander::acquireMediaDevice so that the media devices can be
registered with the pipeline handler, so that they can be automatically
added to the devnum map for the v4l2 compatibility layer to use. Die
fatally if any camera trying to be registered has not acquired any media
devices via acquireMediaDevice.

Signed-off-by: Paul Elder <paul.elder@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

src/libcamera/pipeline_handler.cpp

@@ -496,6 +496,10 @@ void PipelineHandler::registerCamera(std::shared_ptr<Camera> camera,
 	cameraData_[camera.get()] = std::move(data);
 	cameras_.push_back(camera);
 
+	if (mediaDevices_.empty())
+		LOG(Pipeline, Fatal)
+			<< "Registering camera with no media devices!";
+
 	/*
 	 * Walk the entity list and map the devnums of all capture video nodes
 	 * to the camera.