Debugger: Call stack sometimes wrong after 'Pause' on Linux

## Environment data
`dotnet --info` output:
- .NET Core SDK: 1.0.0-preview2-1-003177
- OS Name: rhel
- OS Version: 7.2
- OS Platform: Linux
- RID: rhel.7.2-x64

VS Code version: v1.13.1
C# Extension version: v1.12.0-beat1

## Steps to reproduce

1. Open attached folder.
[hwapp.zip](https://github.com/OmniSharp/omnisharp-vscode/files/1118826/hwapp.zip)

2. Select '.NET Core Attach'.
3. Run 'dotnet run' command in termnal.
4. Press F5 to select process and start debugging.
5. Press 'Pause'

## Expected behavior
The cursor should be hit the current line contains text 'Thread.Sleep(1000);' and Call Stack window should be as following:

## Actual behavior
The cursor didn't hit any line and the Call Stack frame is incorrectly:

[log.txt](https://github.com/OmniSharp/omnisharp-vscode/files/1119146/log.txt)