Unable to get osltoy working

**Describe the bug**

Building osltoy executable works, but it doesn't do anything when run. It opens the window, but shaders are neither compiled, nor run.

**OSL version and dependencies**

* OSL branch/version: 1.13.12.0.2
* OS: Rocky Linux release 9.4
* C++ compiler: clang-15.0.7.3
* LLVM version: llvm-15.0.7.1
* OIIO version: OpenImageIO-2.4.13.0.4
* Qt version: Qt-5.15.3.8

**To Reproduce**

Steps to reproduce the behavior:
1. Build OSL with USE_QT=ON and DISABLE_OSLTOY=OFF
2. Run the osltoy executable
3.
4. Whereas I expected the shader to show uniform grey in the output window.

**Evidence**

- Error messages (paste them here exactly)
`QLayout: Attempting to add QLayout "" to OSL_v1_13::OSLToyMainWindow "", which already has a layout`
- Also during compilation I get the following warnings:
```
/scratch/dev/OpenShadingLanguage/src/testshade/optixgridrender.cpp:999:29: warning: variable 'i' set but not used [-Wunused-but-set-variable]
for (size_t i = 0; !format_end_found; i++) {
^
/scratch/dev/OpenShadingLanguage/src/testshade/optixgridrender.cpp:999:29: warning: variable 'i' set but not used [-Wunused-but-set-variable]
for (size_t i = 0; !format_end_found; i++) {
```
These should be switched for while statements. I'll make a separate PR for this.

- Example shader code (if applicable)
```
shader thing
(
output color Cout = 0.5
)
{
}
```

It'd be great for someone else to confirm they can reproduce this behavior, thanks!

Reproduce the issue by building with USE_QT=ON and DISABLE_OSLTOY=OFF, then run the osltoy executable with the example shader. Start at the osltoy entry point and investigate why the shader is not compiled or run alongside the reported QLayout warning. Done means the shader displays uniform grey in the output window without the layout error.

Written by the indexing model from the issue text.