wined3d: Make sure we have an active GL context in delete_opengl_contexts().

dlls/wined3d/device.c

@@ -6971,6 +6971,8 @@ void delete_opengl_contexts(IWineD3DDevice *iface, IWineD3DSwapChain *swapchain_
     UINT i;
     IWineD3DBaseShaderImpl *shader;
 
+    ActivateContext(This, This->lastActiveRenderTarget, CTXUSAGE_RESOURCELOAD);
+
     IWineD3DDevice_EnumResources(iface, reset_unload_resources, NULL);
     LIST_FOR_EACH_ENTRY(shader, &This->shaders, IWineD3DBaseShaderImpl, baseShader.shader_list_entry) {
         This->shader_backend->shader_destroy((IWineD3DBaseShader *) shader);