Killing a split terminal causes a visual bug in non-default themes

[miguelsolorio]

Issue Type: Bug

Originally was testing #52835 but this repros on the insiders build so unsure if it's related.

Whenever you split a terminal and then proceed to kill it, there is a visual bug on the right side of the terminal that only appears in our non-default (dark/light) themes. This goes away when you move focus away.

VS Code version: Code - Insiders 1.25.0-insider (368ab9c, 2018-06-26T05:11:12.670Z)
OS version: Darwin x64 17.6.0

System Info

Item	Value
CPUs	Intel(R) Core(TM) i7-4770HQ CPU @ 2.20GHz (8 x 2200)
GPU Status	2d_canvas: enabled flash_3d: enabled flash_stage3d: enabled flash_stage3d_baseline: enabled gpu_compositing: enabled multiple_raster_threads: enabled_on native_gpu_memory_buffers: enabled rasterization: enabled video_decode: enabled video_encode: enabled vpx_decode: enabled webgl: enabled webgl2: enabled
Load (avg)	2, 3, 3
Memory (System)	16.00GB (0.20GB free)
Process Argv	/Applications/Visual Studio Code - Insiders.app/Contents/MacOS/Electron -psn_0_3789725
Screen Reader	no
VM	0%

Extensions (4)

Extension	Author (truncated)	Version
svgo	100	0.8.0
vscode-svgo	ajh	0.1.0
gitlens	eam	8.4.1
python	ms-	2018.6.0

(3 theme extensions excluded)

[Tyriar]

Duplicate #51094