IndexError: list index out of range

[Hugh Warrington]

I had been running s-tui in a terminal for several hours without issue.

I returned to the open terminal and saw the process had exited:

```
hugh@goat:~$ s-tui
Traceback (most recent call last):
  File "/usr/bin/s-tui", line 11, in <module>
    load_entry_point('s-tui==1.0.0b3', 'console_scripts', 's-tui')()
  File "/usr/lib/python3/dist-packages/s_tui/s_tui.py", line 882, in main
    graph_controller.main()
  File "/usr/lib/python3/dist-packages/s_tui/s_tui.py", line 738, in main
    loop.run()
  File "/usr/lib/python3/dist-packages/urwid/main_loop.py", line 286, in run
    self._run()
  File "/usr/lib/python3/dist-packages/urwid/main_loop.py", line 384, in _run
    self.event_loop.run()
  File "/usr/lib/python3/dist-packages/urwid/main_loop.py", line 788, in run
    self._loop()
  File "/usr/lib/python3/dist-packages/urwid/main_loop.py", line 821, in _loop
    alarm_callback()
  File "/usr/lib/python3/dist-packages/urwid/main_loop.py", line 172, in cb
    callback(self, user_data)
  File "/usr/lib/python3/dist-packages/s_tui/s_tui.py", line 829, in animate_graph
    self.view.update_displayed_information()
  File "/usr/lib/python3/dist-packages/s_tui/s_tui.py", line 252, in update_displayed_information
    graph.update()
  File "/usr/lib/python3/dist-packages/s_tui/sturwid/bar_graph_vector.py", line 173, in update
    self.graph_data[graph_idx], current_reading[graph_idx])
IndexError: list index out of range
```

At some point I had open and closed my laptop lid, causing it the suspend (maybe, that's also unreliable on my UX433FA which is a separate issue), and also perhaps connected and disconnected some external peripherals. I only mention that because there is an [upstream issue](https://github.com/amanusk/s-tui/issues/144) related to changing hardware (NB that bug report has a different stack trace).

ProblemType: Bug
DistroRelease: Ubuntu 20.04
Package: s-tui 1.0.0-1
ProcVersionSignature: Ubuntu 5.4.0-33.37-generic 5.4.34
Uname: Linux 5.4.0-33-generic x86_64
ApportVersion: 2.20.11-0ubuntu27.2
Architecture: amd64
CasperMD5CheckResult: skip
CurrentDesktop: ubuntu:GNOME
Date: Tue Jun 9 22:01:58 2020
InstallationDate: Installed on 2019-11-07 (215 days ago)
InstallationMedia: Ubuntu 18.04.3 LTS "Bionic Beaver" - Release amd64 (20190805)
PackageArchitecture: all
SourcePackage: s-tui
UpgradeStatus: Upgraded to focal on 2020-06-08 (1 days ago)