When zooming metrics, at some point, we can't adjust the zoom any further

Summary

When zooming in on metric data, evnetually we'll throw a javascript error and zooming via the scroll wheel stops working entirely.

Steps to reproduce

Navigate to a metric dashboard which contains metrics and use the scroll wheel to zoom in and out. Eventually it'll stop working.

What is the current bug behavior?

Zooming stops working entirely.

What is the expected correct behavior?

Zooming should continue.

Relevant logs and/or screenshots

monitor_helper.js:17 Uncaught TypeError: undefined is not iterable (cannot read property Symbol(Symbol.iterator))
    at monitor_helper.js:17
    at b (monitor_helper.js:17)
    at time_series.vue:211
    at Array.forEach (<anonymous>)
    at a.formatTooltipText (time_series.vue:211)
    at a.onLabelChange (charts.js:1350)
    at d (viewHelper.js:177)
    at u (viewHelper.js:79)
    at Object.t.buildCartesianSingleLabelElOption (viewHelper.js:202)
    at n.makeElOption (CartesianAxisPointer.js:69)

Output of checks

GitLab.com