Ignore errors when trying to open the file picker

xdg-desktop-portal-gtk sends a response code essentially indicating that
it failed to open the file picker[0] when you close the file picker without
using the Cancel button[1]. There does not seem to be any way for the portal
to indicate any other kinds of exit conditions aside from success, cancel, or
failure[2].

Additionally, Kotatogram[3] and Firefox[4] does not display an error if the
portal cannot bring up the file picker.

[0] dc8e1d1138/src/filechooser.c (L230)
[1] https://docs.gtk.org/gtk3/enum.ResponseType.html#delete_event
[2] https://flatpak.github.io/xdg-desktop-portal/#gdbus-signal-org-freedesktop-portal-Request.Response
[3] 5b6f711b6d/Telegram/SourceFiles/platform/linux/linux_xdp_file_dialog.cpp (L622)
[4] https://searchfox.org/mozilla-central/rev/42747dfd314e4c939dc7c33a13e1a2fddf4926fc/widget/gtk/nsFilePicker.cpp#590

fragments/export.cpp

@@ -113,7 +113,7 @@ static inline std::optional<File> save_file_picker() {
     } else if (res == NFD_CANCEL) {
         // dialog was canceled, shrug
     } else {
-        log(std::string("Failed to open file picker: ") + NFD_GetError());
+        // ignore error when failing to open the file picker
     }
 
     return std::nullopt;