DNN-30135 - Issue when loading the Persona Bar: Not Thread Safe

[berkarslan-xo]

Note: This is the duplicate PR of dnnsoftware/Dnn.AdminExperience#1126 . I do it again now since it wasn't merged here after Dnn.AdminExperience is migrated here.

Fixes dnnsoftware/Dnn.AdminExperience#1125

Summary
The problem lies in "Dnn.PersonaBar.Library.Repository.PersonaBarRepository.GetMenuItem(string identifier)" method which is called from "Evoq.PersonaBar.UI.Controllers.EvoqPersonaBarContainer.Initialize(UserControl personaBarControl)". GetMenuItem method doesn't exist in the StackTrace because JIT (Just-In-Time) Compiler does Inline Code Optimizations for release builds which basically means that some methods (especially like the ones that are only a few lines) get inlined into the previous method chain for performance reasons. Therefore, if you have a method call chain like A -> B -> C, it might become A -> B if C is inlined (you might think of it as method C's code gets copied under method B).

Using a list instance which might change state in loops (FirstOrDefault method iterates the elements one by one which behaves like a loop) will raise that error when the list gets updated while iterating. The solution is to use ToList method to copy the list's current state into another list and then use it instead for iteration. You can watch the following video I shot a demo video which demonstrates the issue: https://drive.google.com/open?id=13bneeDRu2aqicSvJ-QtV2okoPUivkHh4

[bdukes]

Looks like this was merged into the development branch of Dnn.AdminExperience previously (56fe843). What's our 9.5.1 timeline, are we accepting hotfixes like this? @valadas @mitchelsellers

[mitchelsellers]

@bdukes Lets chat at the meeting today

[berkarslan-xo]

Please note that I raised this PR since @v-karbovnichy asked me to.

[valadas]

Looks good to me