Fixed file name truncating when file is located in the root of the disk

[DenisNikulin5]

In this commit, I fixed an issue when the file name is truncated when it is located in the root of the disk.
It's only related to artifact.upload logging command.

Related GH work item: #4256

Testing: Manual

• Test Pipeline - azure-pipelines.yml:

trigger:
- master

pool: Default

steps:
- powershell: |
    Write-Host "Test > C:\test.txt"
    Write-Host "##vso[artifact.upload artifactname=Test]C:\test.txt"
  displayName: 'Run script'

• Before the fix
  

• After the fix