NaN is shown for percentage change when line is hidden

[colincadams]

Describe the bug

If there is data for a line but it is hidden by the time view selector, e.g. data for one line ends more than a year before data for a different line, then the percentage change for that line shows NaN

To Reproduce Steps to reproduce the behavior:

These are the same steps as #46, except with time scale left at "1 year"

1. Replace src/data.json with https://drive.google.com/file/d/1OLenZP9LW_p3SKX1kA7JahL7n6R-nuxk/view?usp=sharing
2. Change stateCode to US_CT in src/index.js
3. Run yarn start
4. Open the site and scroll to population graph
5. Notice the probation population percentage is NaN

Expected behavior

@hobuobi mentioned that we should use the "No Data Available" treatment for the given line while it is not in view

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Desktop (please complete the following information):

• OS [e.g. Windows 10]: MacOS
• Browser [e.g. chrome, edge]: Chrome
• Version [e.g. 22]:

Additional context Add any other context about the problem here.