Fatal error when closing a notification that has already cleared

[liza-mae]

Kibana version: 6.3.0 BC6
Elasticsearch version: 6.3.0 BC6
Server OS version: OSX
Browser version: Chrome / Firefox
Browser OS version: Latest
Original install method (e.g. download page, yum, from source, etc.): Staging

Describe the bug:
I noticed when closing a notification if you accidentally double click the 'X' or if the system is slow when you click to close the notification and it processes the action after it has cleared you get a fatal error. Seems like something we should handle more gracefully.

Error: Uncaught TypeError: Cannot read property 'clear' of undefined (https://localhost:5605/bundles/vendors.bundle.js:149)
at window.onerror (commons.bundle.js:3)
fatalError @ commons.bundle.js:3
window.onerror @ commons.bundle.js:3
setTimeout (async)
EuiGlobalToastList._this.dismissToast @ vendors.bundle.js:149
Ja @ vendors.bundle.js:141
invokeGuardedCallback @ vendors.bundle.js:149
invokeGuardedCallbackAndCatchFirstError @ vendors.bundle.js:149
Za @ vendors.bundle.js:141
cb @ vendors.bundle.js:141
gb @ vendors.bundle.js:141
ab @ vendors.bundle.js:141
lb @ vendors.bundle.js:141
sd @ vendors.bundle.js:149
rd @ vendors.bundle.js:141
batchedUpdates @ vendors.bundle.js:141
tc @ vendors.bundle.js:141
vd @ vendors.bundle.js:141

Steps to reproduce:

Install Elasticsearch, Kibana
Cause an event to generate a notification, example: clock generate report on dashboard page
Click on the notification 'X' to make it go away , click it twice to cause the error

[chandlerprall]

I can replicate in the Toast docs and is a bug in EUI. I'll bundle this and the EUI fix for #19285 into a special bugfix release in EUI as soon as this is fixed.

[nreese]

closed by #19361