Underlined Letters in Custom Titlebar Appear as Boxes

[McPrescott]

Issue Type: Bug

The screenshot captures the issue better than my description. It seems as if the underline glyph is missing from a font, the same box is shown when I receive texts containing emojis that my phone doesn't recognize.

VS Code version: Code 1.25.0 (0f080e5, 2018-07-05T13:10:37.273Z)
OS version: Linux x64 4.15.0-24-generic

System Info

Item	Value
CPUs	Intel(R) Core(TM) i5-4210U CPU @ 1.70GHz (4 x 1749)
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: disabled_software rasterization: disabled_software video_decode: unavailable_software video_encode: enabled vpx_decode: unavailable_software webgl: enabled webgl2: enabled
Load (avg)	0, 0, 1
Memory (System)	7.67GB (0.40GB free)
Process Argv	/usr/share/code/code --unity-launch
Screen Reader	no
VM	0%