Fix T84049: Crash when using Cycles Progressive Refine with OptiX+CPU

Tile stealing may steal a CPU tile buffer and move it to the GPU, but next time around that
tile may be re-used on the CPU again (in progressive refinement mode). The buffer would
still be on the GPU then though, so is inaccessible to the CPU. As a result Blender crashed
when the CPU tried to write results to that tile buffer.
This fixes that by ensuring a stolen tile buffer is moved back to the device it is used on before
rendering.

intern/cycles/render/session.cpp

@@ -540,6 +540,10 @@ bool Session::acquire_tile(RenderTile &rtile, Device *tile_device, uint tile_typ
     tile->buffers = new RenderBuffers(tile_device);
     tile->buffers->reset(buffer_params);
   }
+  else if (tile->buffers->buffer.device != tile_device) {
+    /* Move buffer to current tile device again in case it was stolen before. */
+    tile->buffers->buffer.move_device(tile_device);
+  }
 
   tile->buffers->map_neighbor_copied = false;