After updated to 1.33.0, loading 'markdown.styles' setting is getting failed

[rykoma]

Issue Type: Bug

1. Create workspace setting like below.

{
	"folders": [
		{
			"path": "."
		}
	],
	"settings": {
		"markdown.styles": ["md-preview.css"]
	}
}

2. Create md-preview.css and save it to the same path as the workspace setting file.

3. Update to 1.33.0.

4. Show the preview of markdown file.

Expected behavior:
The preview of markdown file is styled with css file.

Actual behavior:
A toast will be displayed and it says "Could not load 'markdown.styles': md-preview.css".

VS Code version: Code 1.33.0 (0dd516d, 2019-04-04T15:14:28.026Z)
OS version: Windows_NT x64 10.0.17763

System Info

Item	Value
CPUs	Intel(R) Core(TM) i5-6300U CPU @ 2.40GHz (4 x 2496)
GPU Status	2d_canvas: enabled checker_imaging: disabled_off flash_3d: enabled flash_stage3d: enabled flash_stage3d_baseline: enabled gpu_compositing: enabled multiple_raster_threads: enabled_on native_gpu_memory_buffers: disabled_software rasterization: enabled surface_synchronization: enabled_on video_decode: enabled webgl: enabled webgl2: enabled
Memory (System)	7.93GB (3.24GB free)
Process Argv	C:\Users\rykoma\OneDrive - Microsoft\SR\SR.code-workspace
Screen Reader	no
VM	0%

Extensions (1)

Extension	Author (truncated)	Version
csharp	ms-	1.18.0

[mjbvz]

Duplicate of #71802

[sakronos]

Duplicate of #71802

The bug still exists in version 1.33.1