Handle file tasks case-insensitively

[CommandMC]

Resolves #689 Can't test this myself as I don't own that game; regular downloads still seem to work fine

This'll probably cause issues with macOS-native games, not sure how/if we want to handle that

[Etaash-mathamsetty]

Is it possible to check if the game is Mac os native and if it is just use the original code ?