Use safe library function tailSafe instead of locally-defined tailOrEmpty.

[jonathanknowles]

Issue Number

None. But spotted while looking at issue #674.

Overview

This replaces a hand-written function with a function from the safe library (which we already use elsewhere).

[Anviking]

Is it really worth using a library for the sake of replacing one trivial function though?

[jonathanknowles]

Is it really worth using a library for the sake of replacing one trivial function though?

We already use this library in other places in our code-base.

I'd argue it's better to use a commonly-used library than to keep on redefining these functions. The safe library is already pretty widely used. People are already familiar with functions like headMay, lastMay, tailSafe and so on.