Don't remove url suffix when suggestion is selected

[bbondy]

The bug is because of this section in urlBar component's componentDidUpdate:

    } else if (this.props.autocompleteEnabled &&
        this.props.normalizedSuggestion !== prevProps.normalizedSuggestion) {
      this.updateAutocomplete(this.lastVal)
    // This case handles when entering urlmode from tilemode
    }

In this case there is no suggestion because we emptied it out so we shouldn't clear what the user typed in yet.

Fix #11060

Submitter Checklist:

• Submitted a ticket for my issue if one did not already exist.
• Used Github auto-closing keywords in the commit message.
• Added/updated tests for this change (for new code or code which already has tests).
• Ran git rebase -i to squash commits (if needed).
• Tagged reviewers and labelled the pull request as needed.

Test Plan:

Reviewer Checklist:

Tests

• Adequate test coverage exists to prevent regressions
• Tests should be independent and work correctly when run individually or as a suite ref
• New files have MPL2 license header

[NejcZdovc]

++

[bsclifton]

0.19.x c9ed9e7
0.20.x ec2f647

@bbondy @NejcZdovc I don't think this should this be merged to master, should it?

[bbondy]

It was needed for master as well, merged it here:
9874f96