Fix alternating tint logic when blocks are hidden

[ammgws]

Fixes #349

@GladOSkar would you like to give it a go and see if it's fixed? Testing with the below config showed the colours match the current behaviour so I assume it's working:

[theme]
name = "slick"
[theme.overrides]
separator = "SEPARATOR"

[icons]
name = "awesome"

[[block]]
block = "time"

[[block]]
block = "time"

[[block]]
block = "time"

[[block]]
block = "time"

[GladOSkar]

Yes it works beautifully, thank you!

[GladOSkar]

I wonder if it would make more sense to do the alternating from right to left than from left to right, since the right is basically the anchor of the status bar.

Currently, whenever a network device shows up or disappears on my system, the alternating color stays the same on the left of that block and flips on the right. I'd rather have it the other way around