GPU D3D12: Fix command buffer leak

src/gpu/d3d12/SDL_gpu_d3d12.c

@@ -1230,6 +1230,7 @@ static void D3D12_INTERNAL_DestroyCommandBuffer(D3D12CommandBuffer *commandBuffe
     SDL_free(commandBuffer->usedGraphicsPipelines);
     SDL_free(commandBuffer->usedComputePipelines);
     SDL_free(commandBuffer->usedUniformBuffers);
+    SDL_free(commandBuffer->textureDownloads);
     SDL_free(commandBuffer);
 }