[BUG] Bad output indices from `pointcloud_search()` with batched shading

**Describe the bug**

When using `pointcloud_search()` with batched shader execution, the output `indices` array is not being filled correctly. It looks a little like OSL thinks the output is a uniform rather than a varying value, but I don't know enough about what is going on under the hood to be sure.

**OSL version and dependencies**

* OSL branch/version: 1.14.5.1
* OS: Rocky 8.8
* C++ compiler: GCC 11.2.1
* LLVM version: 15.0.7
* OIIO version: 3.0.6.1

**To Reproduce**

Steps to reproduce the behavior:

1. `oslc search.osl` (source code in section below).
2. `testshade -g 16 16 -batched -param file cloud.geo search.oso -o Cout batched.png`
3. `testshade -g 16 16 -param file cloud.geo search.oso -o Cout unbatched.png`
4. Compare `batched.png` to `unbatched.png`. The latter has the expected results, and the former does not.

In the above commands, `cloud.geo` is `testsuite/pointcloud-fold/cloud.geo` from the OSL repo.

**Evidence**

search.osl

```
shader search( string file = "", output color Cout = 0 )
{
int indices[1];

// Uncommenting this workaround gives the expected results in batched
// mode. I suspect it works by tricking OSL into realising that `indices`
// is a varying quantity.
// indices[0] = P[0];

if( pointcloud_search( file, P, 1, 1, "index", indices ) )
{
Cout = color( indices[0] / 15.0 );
}
else
{
Cout = color( 1, 0, 0 );
}
}
```

batched.png :

unbatched.png :

Run the listed oslc and testshade commands using testsuite/pointcloud-fold/cloud.geo, then compare the batched and unbatched output. Start at the pointcloud_search entry point and trace how the output indices array is handled during batched execution. Done means batched.png matches the expected unbatched results without the workaround.

Written by the indexing model from the issue text.