Fix memory leak after using OptiX in Cycles

The "optix_devices" array was not freed on exit, which caused a memory leak (see T69801).

Reviewed By: brecht

Differential Revision: https://developer.blender.org/D5944

intern/cycles/device/device.cpp

@@ -643,6 +643,7 @@ void Device::free_memory()
 {
   devices_initialized_mask = 0;
   cuda_devices.free_memory();
+  optix_devices.free_memory();
   opencl_devices.free_memory();
   cpu_devices.free_memory();
   network_devices.free_memory();