fix: Fix testrender GPU regression with bad destruction order (#1814)

A few months back, PR #1733 seems to have switched the order that
testrender destroys the shading system versus the renderer (services).

This made some subtle bugs that were only symptomatic for GPU renders,
but it's because of the destructor order, where the shadingsystem's
dtr still references the renderer, which cannot be destroyed yet.

The clue is that the SS's constructor takes the RS pointer as an
argument. The RS, then, must have been constructed before the SS, and
therefore we should expect it to be a requirement for the RS to
outlast the lifetime of the SS. (Complex objects should be destroyed
in the opposite order that they were constructed, if they contain
references to each other.)

One code change is needed to avoid the sanitizer errors that the
incorrect change was originally meant to address: clear shaders when
SimpleRayTracer clears.

Signed-off-by: Larry Gritz <lg@larrygritz.com>

---------

Signed-off-by: Larry Gritz <lg@larrygritz.com>

Author: lgritz

src/testrender/optixraytracer.cpp

@@ -1253,7 +1253,7 @@ OptixRaytracer::finalize_pixel_buffer()
 void
 OptixRaytracer::clear()
 {
-    shaders().clear();
+    SimpleRaytracer::clear();
     OPTIX_CHECK(optixDeviceContextDestroy(m_optix_ctx));
     m_optix_ctx = 0;
 }

src/testrender/simpleraytracer.cpp

@@ -1101,4 +1101,10 @@ SimpleRaytracer::render(int xres, int yres)
 
 
 
+void
+SimpleRaytracer::clear()
+{
+    shaders().clear();
+}
+
 OSL_NAMESPACE_EXIT

src/testrender/simpleraytracer.h

@@ -82,7 +82,7 @@ class SimpleRaytracer : public RendererServices {
     virtual void prepare_render();
     virtual void warmup() {}
     virtual void render(int xres, int yres);
-    virtual void clear() {}
+    virtual void clear();
 
     // After render, get the pixels into pixelbuf, if they aren't already.
     virtual void finalize_pixel_buffer() {}

src/testrender/testrender.cpp

@@ -368,7 +368,7 @@ main(int argc, const char* argv[])
 
     // We're done with the shading system now, destroy it
     rend->clear();
-    delete rend;
     delete shadingsys;
+    delete rend;
     return EXIT_SUCCESS;
 }