Ensure directory exists before writing point cloud

Reviewed By: mwerlberger

Differential Revision: D28572540

fbshipit-source-id: d5e432e900442a214b7e1c3cb66de73a8c1bf962

Author: Manuel Lopez Antequera

opensfm/dataset.py

@@ -1208,6 +1208,7 @@ def save_point_cloud(
         detections: np.ndarray,
         filename: str = "merged.ply",
     ) -> None:
+        self.io_handler.mkdir_p(self._depthmap_path())
         with self.io_handler.open(self.point_cloud_file(filename), "w") as fp:
             io.point_cloud_to_ply(points, normals, colors, labels, detections, fp)