d3d9/tests: Keep swapchain while its backbuffer is in use.

dlls/d3d9/tests/stateblock.c

@@ -255,6 +255,7 @@ static void execute_test_chain(
 typedef struct event_data {
     IDirect3DStateBlock9* stateblock;
     IDirect3DSurface9* original_render_target;
+    IDirect3DSwapChain9* new_swap_chain;
 } event_data;
 
 static int switch_render_target(
@@ -293,7 +294,7 @@ static int switch_render_target(
     if (hret != D3D_OK) goto error;
 
     IUnknown_Release(backbuffer);
-    IUnknown_Release(swapchain);
+    edata->new_swap_chain = swapchain;
     return EVENT_OK;
 
     error:
@@ -318,6 +319,8 @@ static int revert_render_target(
     }
 
     IUnknown_Release(edata->original_render_target);
+
+    IUnknown_Release(edata->new_swap_chain);
     return EVENT_OK;
 }