Terminating a background task switches terminal selector to ----- and crashes VSCode

[jakubdrozdek]

Issue Type: Bug

Steps to reproduce:

1. Run a background task, e.g. TypeScript compiler in watch mode
2. Open a new terminal.
3. Terminate the background task.

Expected result:
Terminal should switch to the open terminal.

Actual result:
Terminal selector changes to "------" (the divider) and sometimes freezes VSCode.

VS Code version: Code 1.48.2 (a047975, 2020-08-25T10:13:11.295Z)
OS version: Windows_NT x64 10.0.19041

System Info

Item	Value
CPUs	Intel(R) Core(TM) i5-2500K CPU @ 3.30GHz (4 x 3310)
GPU Status	2d_canvas: enabled flash_3d: enabled flash_stage3d: enabled flash_stage3d_baseline: enabled gpu_compositing: enabled multiple_raster_threads: enabled_on oop_rasterization: disabled_off protected_video_decode: unavailable_off rasterization: enabled skia_renderer: disabled_off_ok video_decode: enabled viz_display_compositor: enabled_on viz_hit_test_surface_layer: disabled_off_ok webgl: enabled webgl2: enabled
Load (avg)	undefined
Memory (System)	11.92GB (5.43GB free)
Process Argv
Screen Reader	no
VM	0%

Extensions (11)

Extension	Author (truncated)	Version
project-manager	ale	11.3.0
better-toml	bun	0.3.2
vscode-eslint	dba	2.1.8
gitlens	eam	10.2.2
EditorConfig	Edi	0.15.1
prettier-vscode	esb	5.5.0
vscode-docker	ms-	1.5.0
vscode-jest	Ort	3.2.0
rust	rus	0.7.8
code-settings-sync	Sha	3.4.3
material-theme	zhu	3.8.7

[alexr00]

For the crash, that is likely #71966
For the terminal selector showing the separator, that is bug that we should fix.