check DialogParent null value + initialize whith standard BackgroundForm

[smart717]

Possible bug fix. If custom profile use WIA with "Use Native UI" option, using NAPS2 with command-line options (-o test.pdf) return an error instead of showing native interface before scanning.

ex: .\NAPS2.Console.exe -o output.pdf

An error occurred with the scanning driver. No scanned pages to export.

With this solution, the native interface is showed and the file is saved correctly