Consider replacing calls to BuildMultipleAssemblyPath when passing only one source

[Evangelink]

There is no need to use BuildMultipleAssemblyPath if we pass only one source, instead we could use GetASsetFullPath.

Originally posted by @Evangelink in #3459 (comment)

[daveMueller]

Is it OK if I work on this and contribute a PR?

[nohwnd]

Thanks @daveMueller!