Convert legacy Inkscape file (dpi switch) dialog only shows up in new window (not new document)

Similar to #3177 (moved) , only it affects a different dialog

Steps to reproduce:

  • Open inkscape with this svg: inkscape-old.svg
  • (Notice Convert legacy Inkscape file dialog)
  • Now open made-up-font.svg again (so it opens a second window)
  • (Notice Convert legacy Inkscape file dialog)
  • Now close both windows, so only a New Document remains
  • Open inkscape-old.svg again (so it replaces the current document, no new window)

What happened?

  • No Convert legacy Inkscape file dialog in the last case

What should have happened?

  • Convert legacy Inkscape file dialog appears in all cases

Example file

inkscape-old.svg inkscape-old.svg

Version Info:

  • 1.1-dev (a9d5e92c4bbf04a4ecc151678855fc6ec6b8146e) custom build Linux Mint 19.1
  • Inkscape 1.0 (6e3e5246a0, 2020-05-07) snap Linux Mint 19.1

but

  • Not replicated Inkscape 0.92.3 (2405546, 2018-03-11) Linux Mint 19.1
  • Not replicated Inkscape 0.92.5 (fe8e1c6569, 2020-04-22) Linux Mint 19.1