Unable to close schematic editor after failed import

Description

If you try to import a schematic that fails, e.g. Interface.sch (which is a binary Eagle file), after the import failure is reported, the schematic editor cannot be closed using any normal method, only a killall closes it. If you just cancel the import at the file selector, the editor can still be closed after. So it appears that something we do after the file selection might be blocking the frame from closing.

Steps to reproduce

1. Launnch the standalone schematic editor.
2. Import a schematic that will fail to import.
3. Try closing the schematic editor (either through the X button or the menu button or Alt-F4).
4. See the window doesn't close.

KiCad Version

Application: KiCad Schematic Editor x86_64 on x86_64

Version: 8.0.0-rc2-583-g206a631135, debug build

Libraries:
	wxWidgets 3.2.4
	FreeType 2.13.1
	HarfBuzz 8.2.1
	FontConfig 2.14.2
	libcurl/8.2.1 OpenSSL/3.1.1 zlib/1.2.13 brotli/1.1.0 libidn2/2.3.4 libpsl/0.21.2 (+libidn2/2.3.4) libssh/0.10.6/openssl/zlib nghttp2/1.55.1 OpenLDAP/2.6.6

Platform: Fedora Linux 39 (MATE-Compiz), 64 bit, Little endian, wxGTK, X11, mate, x11

Build Info:
	Date: Feb 16 2024 11:42:19
	wxWidgets: 3.2.4 (wchar_t,wx containers) GTK+ 3.24
	Boost: 1.81.0
	OCC: 7.6.3
	Curl: 8.2.1
	ngspice: 42
	Compiler: Clang 17.0.6 with C++ ABI 1002

Build settings:
	KICAD_STDLIB_DEBUG=OFF
	KICAD_STDLIB_LIGHT_DEBUG=ON
	KICAD_SANITIZE_ADDRESS=ON
	KICAD_SANITIZE_THREADS=OFF