fix: GridPoseSampler crashes on empty freespace block

[andrewwhitecdw]

This PR addresses the following issue in exts/omni.ext.mobility_gen/omni/ext/mobility_gen/pose_samplers.py: GridPoseSampler crashes on empty freespace block.

Changes

• exts/omni.ext.mobility_gen/omni/ext/mobility_gen/pose_samplers.py: GridPoseSampler crashes on empty freespace block.

Details

Before:

        coords = np.argwhere(net_mask)
        random_index = np.random.randint(0, len(coords))
        pixel = coords[random_index]

After:

        coords = np.argwhere(net_mask)
        if len(coords) == 0:
            raise ValueError("Selected grid block contains no freespace pixels")
        random_index = np.random.randint(0, len(coords))
        pixel = coords[random_index]