Not setting GTK_CSD can break CustomFileChooserDialog in applications

[worldofpeace]

Issue Description

For example, attempting to open a file in vlc results in

(vlc:1306): Gtk-WARNING **: 00:09:56.295: gtk_window_set_titlebar() called on a realized window

And I cannot see a FileChooserDialog drawn and the entire window is unresponsive.

However it works fine in Code and Firefox.

Technical Details

• host os: Linux 4.9.180, NixOS
• files version: 4.1.8
• files build dependencies

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[worldofpeace]

So this apparently is only an issue if you haven't set GTK_CSD=1

See

• https://github.com/elementary/default-settings/pull/103#issuecomment-438613785
• https://github.com/elementary/default-settings/pull/103#issuecomment-440308643

The MR https://gitlab.gnome.org/GNOME/gtk/merge_requests/566 would help with this.