gdiplus: Make get_palette() usable for generating predefined palettes.

dlls/gdiplus/image.c

@@ -76,6 +76,8 @@ static ColorPalette *get_palette(IWICBitmapFrameDecode *frame, WICBitmapPaletteT
     hr = IWICImagingFactory_CreatePalette(factory, &wic_palette);
     if (hr == S_OK)
     {
+        hr = WINCODEC_ERR_PALETTEUNAVAILABLE;
+        if (frame)
             hr = IWICBitmapFrameDecode_CopyPalette(frame, wic_palette);
         if (hr != S_OK)
         {