Problems in Discover and Index Patterns when index doesn't exist

[LeeDr]

Kibana version: 7.6.0-SNAPSHOT

Elasticsearch version: 7.6.0-SNAPSHOT

Server OS version: CentOS 7

Browser version: Chrome 79

Browser OS version: Windows 10

Original install method (e.g. download page, yum, from source, etc.): rpm default dist

Describe the bug: I think there's 2 ways to get into this bad state;

1. Create an index pattern through the saved object API (like beats setup does) but don't create the index
2. delete existing indices behind an existing Kibana index pattern

Then there are 2 problems from this;

1. If you click on the index pattern name in the Index Patterns landing page, you get an error (see screenshots below), and so you can't delete it. (you could still delete it from the Saved Objects UI).
2. If you navigate to Discover and it's going to try to open that index pattern because of either of these cases you get that same error;
   1. It's the default index pattern and you don't have some other discover page cached with a different index pattern
   2. it's the cached index pattern you last opened in Discover

Steps to reproduce:

1. index some data into Elasticsearch
2. create a Kibana index pattern for the data
3. delete the index (make sure nothing is running to re-create the index like metricbeat)
4. go to Discover - the error appears and Discover page doesn't load
5. go back to index patterns and try to select the index pattern to delete it - same error and page doesn't load to allow you to delete it

Expected behavior: In 7.5.2 Discover would just show the no data found message. And you could select a different index pattern in Discover.

Screenshots (if relevant):
This screenshot shows trying to open the packetbeat index pattern when there's no packetbeat index. I get an error and can't delete it from this UI.

This screenshot shows that I set packetbeat-* as the default setting,
then I open discover, but because I may have visited the page on the metricbeat index last, it loads OK. But then I open a new incognito browser window to discover which opens the default packetbeat-* index and fails.

Errors in browser console (if relevant):

Provide logs and/or server output (if relevant):

Any additional context:

[elasticmachine]

Pinging @elastic/kibana-app (Team:KibanaApp)