Fix crash when using Safari Translation feature

[zigcccc]

Summary

This PR is to address an issue where the app would crash (unhandled exception is thrown) in Safari, when the following is true:

• Safari's translation feature is enabled
• at least one LinesEllipsis with and one without truncated text is first rendered on the screen and then unmounted

Steps to reproduce

• Render 2 LinesEllipsis components on the screen; 1 should truncate the text and one should not
  • in my case I set basedOn="letters" but I think that doesn't really play a role
• Open the page in Safari (mobile/desktop doesn't matter)
• Translate the page to something other than what the original language was; make sure that the text inside LinesEllipsis gets translated
• unmount the components
• 💥

Minimal reproducible example

https://github.com/zigcccc/react-lines-ellipsis-crash-minimal-reproducible-example

Demo

React.Lines.Ellipsis.Safari.Crash.mp4

The problem

• for some reason, when Safari applies translations, it manipulates DOM nodes in a way to trigger this.canvas to be null
• in componentWillUnmount, we're assuming that this.canvas is always defined
• since that's not the case, we're accessing property (parentNode) on null, which causes the crash

I'm not sure how exactly that happens, and why this is scoped to Safari only (applying translations in Chrome works without any issues). But simply verifying that we have a canvas element to work with before doing any operations on it prevents the app from crashing, which is the goal of this PR.

[adamjaffeback]

Thanks @zigcccc for opening this PR. We're getting hundreds of errors per week because of this on a payments platform; it's blocking people from collecting a paycheck. Hope @xiaody can help you move fast on this—it's such a minor change. Good find!

[adamjaffeback]

Introduced here #104

[srajchevski]

We've been stuck on this for a while, and just moved it to the backlog...
Would be nice if this could get fixed soon!!

[xiaody]

Released as react-lines-ellipsis@0.15.4. Thx everyone.