Input file path sometimes does not resolve on Windows

- Version: 5.0.1
- Operating System: Windows 8, Windows 10

I witnessed two issues last week with Windows users of Logstash, where the input file path did not resolve when either:
* The drive letter was capitalized. In Windows, users can use both `C:` as well as `c:` in most applications.
* There was a space in the path, even while having quotes around the path

No errors shows, Logstash would just sit idle.

Unfortunately I can't reproduce it myself due to a lack of Windows.