Use less path normalization due to poor performance on Windows

[sfPlayer1]

This removes some theoretically redundant path normalization, only doing some extra validation with asserts enabled (-ea)

Fixes #970

[MCRcortex]

Testing this PR it does feel faster to launch (however this might just be a bias/computer having an ok day)

Profiling it, path normalization is completely eliminated from the profiler.

All threads:

Render thread:

Confirmed this PR removed the bottleneck of path normalization on windows.

Launch time (appears) to be on par with vanilla (no mod loader)

Thank you for the fix!