only clone readonly patches in pc_patch_rotate_quaternion

The cloning of the uncompressed pc_patch is currently done unconditionally in https://github.com/LI3DS/pointcloud/blob/dev/lib/pc_patch.c#L683-L688
This could be performed only when the patch is readonly, taking care of freeing the returned patch only if it differs from the input patch at https://github.com/LI3DS/pointcloud/blob/dev/pgsql/pc_editor.c#L63