Add Support For Timeframe Units With Zero Delta in Icelandic Locale

## Feature Request

Currently we do not have timeframe strings in the Icelandic locale that correspond with a time delta of zero. For example, we do not have a string that represents "0 seconds" in the Icelandic locale. We would like to fix this. For the time being, since we don't cover this case within the Icelandic locale, I think we'll resort to any time delta of 0 corresponding to the future tense of strings.

The issue names no file or test. Start by locating the Icelandic locale definitions and existing timeframe-unit strings, then inspect how zero deltas are represented elsewhere in the project. Done means Icelandic strings cover zero for the relevant timeframe units and the applicable locale tests pass.

Written by the indexing model from the issue text.