fix: getEntityState() for "last" & "bar"

[ildar170975]

Currently using "last" & "bar" causes a card to be not rendered due to an error.

type: custom:mini-graph-card
entities:
  - entity: sensor.system_monitor_processor_use
show:
  state: last
  graph: bar

It happens because "this.points" is not defined if graph type = "bar".

After the fix:

[ildar170975]

So we have 3 PRs to fix the same problem:

1. fix: always get points so state last works with other graphs #1075 - "always define points".
2. fix: state: last to use value from last Graph coordinate #1308 - "use coords"
3. this one - "ether use points or bars".

Currently "points" & "bars" already have properly (I hope so) defined values.
So why not using these data instead?

Imho:

1. Calculating "points" in case of bars is too "artificial".
2. Using "coords" in "main()" is too "low level" because "coords" are inside a Graph object, I do not think we are supposed to use them directly in "main()".

[akloeckner]

Imho:

On the conceptual level, I'd agree. I'm wondering: will this fix also work, if show.points is false? (I think, that is a valid option, right?)