panic on macOS

[danielskowronski]

On macOS it fails immediately after connecting to VNC server.

~/var/vnc-recorder macbook $ /usr/local/bin/ffmpeg -version 
ffmpeg version 4.4.1 Copyright (c) 2000-2021 the FFmpeg developers
built with Apple clang version 13.0.0 (clang-1300.0.29.3)
configuration: --prefix=/usr/local/Cellar/ffmpeg/4.4.1_5 --enable-shared --enable-pthreads --enable-version3 --cc=clang --host-cflags= --host-ldflags= --enable-ffplay --enable-gnutls --enable-gpl --enable-libaom --enable-libbluray --enable-libdav1d --enable-libmp3lame --enable-libopus --enable-librav1e --enable-librist --enable-librubberband --enable-libsnappy --enable-libsrt --enable-libtesseract --enable-libtheora --enable-libvidstab --enable-libvmaf --enable-libvorbis --enable-libvpx --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxml2 --enable-libxvid --enable-lzma --enable-libfontconfig --enable-libfreetype --enable-frei0r --enable-libass --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-libspeex --enable-libsoxr --enable-libzmq --enable-libzimg --disable-libjack --disable-indev=jack --enable-avresample --enable-videotoolbox
libavutil      56. 70.100 / 56. 70.100
libavcodec     58.134.100 / 58.134.100
libavformat    58. 76.100 / 58. 76.100
libavdevice    58. 13.100 / 58. 13.100
libavfilter     7.110.100 /  7.110.100
libavresample   4.  0.  0 /  4.  0.  0
libswscale      5.  9.100 /  5.  9.100
libswresample   3.  9.100 /  3.  9.100
libpostproc    55.  9.100 / 55.  9.100
~/var/vnc-recorder macbook $ ./vnc-recorder --host localhost --port 5999 --ffmpeg /usr/local/bin/ffmpeg
INFO[0000] connection established.                       address="localhost:5999"
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x18 pc=0x114588e]

goroutine 1 [running]:
github.com/amitbet/vnc2video.(*DefaultClientSecurityHandler).Handle(0x12a4f88, {0x12a6648, 0xc000222500})
	/Users/dskowronski/go/pkg/mod/github.com/amitbet/[email protected]/handlers.go:150 +0x24e
github.com/amitbet/vnc2video.Connect({0xc000206070, 0x124fe73}, {0x12a4f88, 0xc000188000}, 0xc000220000)
	/Users/dskowronski/go/pkg/mod/github.com/amitbet/[email protected]/client.go:38 +0x1c5
main.recorder(0xc0001b8000)
	/Users/dskowronski/var/vnc-recorder/main.go:130 +0x875
github.com/urfave/cli/v2.(*App).RunContext(0xc0001b6000, {0x12a12d0, 0xc00012c008}, {0xc000130000, 0x7, 0x7})
	/Users/dskowronski/go/pkg/mod/github.com/urfave/cli/[email protected]/app.go:315 +0x8ac
github.com/urfave/cli/v2.(*App).Run(...)
	/Users/dskowronski/go/pkg/mod/github.com/urfave/cli/[email protected]/app.go:215
main.main()
	/Users/dskowronski/var/vnc-recorder/main.go:77 +0x709
~/var/vnc-recorder macbook $