Don't crash on the L5

src/io_pipeline.c

@@ -382,6 +382,11 @@ update_state(MPPipeline *pipeline, const struct mp_io_pipeline_state *state)
                                         mode_capture = io_camera->modes[m];
                                 }
                         }
+                        if (mode_preview == NULL && mode_capture != NULL) {
+                                // If no fast preview mode is available, make do with
+                                // slow modes.
+                                mode_preview = mode_capture;
+                        }
                         if (mode_preview != NULL) {
                                 if (io_camera->video_fd == 0) {
                                         libmegapixels_open(io_camera);