Fix crash on some games using DX11.

The line: "ctx->PSGetSamplers(0, 1, &old.PSSampler);" will fail silently (no return code) but will not modify old.PSSampler making the game crash when accessing uninitialized memory.

ImGui/impls/windows/imgui_impl_dx11.cpp

@@ -194,7 +194,7 @@ void ImGui_ImplDX11_RenderDrawData(ImDrawData* draw_data)
         DXGI_FORMAT                 IndexBufferFormat;
         ID3D11InputLayout*          InputLayout;
     };
-    BACKUP_DX11_STATE old;
+    BACKUP_DX11_STATE old = {};
     old.ScissorRectsCount = old.ViewportsCount = D3D11_VIEWPORT_AND_SCISSORRECT_OBJECT_COUNT_PER_PIPELINE;
     ctx->RSGetScissorRects(&old.ScissorRectsCount, old.ScissorRects);
     ctx->RSGetViewports(&old.ViewportsCount, old.Viewports);