Do not apply sanitization to root path when generating paths for downloaded assets in the cache folder

[fthevenet]

This PR aims to address issue #972

Application launched via a JNLP file will failed to start for user wtih certain characters in their home folder (e.g. C:\Users\Foo_O'Bar), which is a legal path on Windows, but paths for downloaded asset are incorrectly sanitize as C:\Users\Foo_O_Bar and the application then fails as it attempts to access content in C:\Users\Foo_O_Bar\... instead of C:\Users\Foo_OBar...

[janakmulani]

@fthevenet we think removing the character "'" from INVALID_PATH list in FileUtils.java should fix the issue of "Foo_O'Bar" as "'" is a valid character for filepath in Windows. Can you please try this fix and resubmit the PR?

[fthevenet]

I don't think this is the right approach even though it would indeed fix this particular occurrence.
For example, the same problem would arise with a root path for the cache folder containing the character : on Linux, which, while legal on this file system, would be incorrectly sanitized and result in the same FileNotFoundException.

On the other hand, I think the root parameter used by the method should always contain a path that is legal for the runtime platform, since it is derived from system properties or supplied by the user via a property, so sanitizing this part of the path gains us nothing anyway.