Gerber export crashes for sketched pads on fabrication layer if pad dimensions are <= plotting line width

Description

GERBER_PLOTTER::FlashPadRoundRect crashes with assertion failure (with -DKICAD_STDLIB_LIGHT_DEBUG=1) when plotting fabrication layers with sketch pads enabled if the pad size is equal or smaller than the plotting line size.

outline.Outline( 0 ); assumes the presence of one point, but outline.Inflate() just above can remove all points of the pad.

https://gitlab.com/kicad/code/kicad/-/blob/master/common/plotters/GERBER_plotter.cpp#L1490

Steps to reproduce

1. Compile with -DKICAD_STDLIB_LIGHT_DEBUG=1
2. Use small custom pad on footprint e.g. 0.1mm*0.1mm
3. Export fabrication layer with sketch pads enabled

KiCad Version

Application: KiCad

Version: (6.0.4), release build

Libraries:
	wxWidgets 3.0.5
	libcurl/7.82.0 OpenSSL/1.1.1n zlib/1.2.12 brotli/1.0.9 zstd/1.5.2 libidn2/2.3.2 libpsl/0.21.1 (+libidn2/2.3.0) libssh2/1.10.0 nghttp2/1.47.0

Platform: Linux 5.17.4-arch1-1 x86_64, 64 bit, Little endian, wxGTK, xmonad, x11

Build Info:
	Date: Mar 18 2022 08:05:28
	wxWidgets: 3.0.5 (wchar_t,wx containers,compatible with 2.8) GTK+ 3.24
	Boost: 1.78.0
	OCC: 7.5.3
	Curl: 7.82.0
	ngspice: 36
	Compiler: GCC 11.2.0 with C++ ABI 1016

Build settings:
	KICAD_USE_OCC=ON
	KICAD_SPICE=ON