UI hang when performing schematic edit actions on network shares

This issue is due to the file I/O activity cause by checking file existence and read only status when SCH_EDIT_FRAME::UpdateTitle() is called to update the modified indicator(*) in the title bar.

Description

This issue is related to and discuss in issue #9278 (closed).

Steps to reproduce

1. Open a schematic on a network share and perform any edit operation.
2. Observe UI hang proportional to the network speed.

KiCad Version

Application: KiCad Schematic Editor

Version: (5.99.0-12735-gae0229b7c9), debug build

Libraries:
	wxWidgets 3.0.5
	libcurl/7.74.0 GnuTLS/3.7.2 zlib/1.2.11 brotli/1.0.9 libidn2/2.3.2 libpsl/0.21.0 (+libidn2/2.3.0) libssh2/1.9.0 nghttp2/1.43.0 librtmp/2.3

Platform: Linux 5.14.0-1-amd64 x86_64, 64 bit, Little endian, wxGTK, default, x11

Build Info:
	Date: Oct  8 2021 15:44:26
	wxWidgets: 3.0.5 (wchar_t,wx containers,compatible with 2.8) GTK+ 3.24
	Boost: 1.74.0
	OCC: 7.5.1
	Curl: 7.74.0
	ngspice: 34
	Compiler: GCC 10.3.0 with C++ ABI 1014

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