Duplicate LR line if the bottom edge only has one line available

Fixes #227.
14 jobs for master in 6 minutes and 8 seconds (queued for 3 seconds)
Status Job ID Name Coverage
  Style
passed #245319
amd64 debian
style-check

00:00:20

 
  Build
passed #245320
amd64 debian
build-debian

00:00:31

passed #245325
debian aarch64
build-debian-aarch64

00:01:35

passed #245326
debian aarch64
build-debian-aarch64-clang-5

00:01:11

passed #245321
amd64 debian
build-debian-static

00:00:34

passed #245328
debian aarch64
build-debian-werror

00:00:40

passed #245322
amd64 debian
build-debian32

00:00:28

passed #245327
macos
build-macos

00:00:27

passed #245323
win32
build-win32

00:00:28

passed #245324
win64
build-win64

00:00:38

 
  Test
passed #245329
amd64 debian
test-debian

00:00:43

passed #245330
amd64 debian
test-debian-asan

00:02:08

passed #245331
amd64 debian
test-debian-msan

00:00:57

passed #245332
amd64 debian
test-debian-ubsan

00:01:18