Crash from LSR

Hi Chris,
We found there are crash from here
in LSR, DynamicCompilationBase.cs:66

```
AssemblyCsharpFullPath = SessionStateCache.GetOrCreateString(
$"FSR:AssemblyCsharpFullPath",
() => AssetDatabase.FindAssets("Microsoft.CSharp")
.Select(g => new System.IO.FileInfo(UnityEngine.Application.dataPath + "/../" + AssetDatabase.GUIDToAssetPath(g)))
.First(fi => fi.Name.ToLower() == "Microsoft.CSharp.dll".ToLower()).FullName
```
`Sequence contains no matching element

Microsoft.CSharp wont find anything in assets as FSR is in package

We tried this
`() => AssetDatabase.FindAssets("Microsoft.CSharp", new string[]{ "Packages", "Assets"})`

from https://discussions.unity.com/t/assetdatabase-findassets-not-working-for-packages/707087/10

But seems it was not enough and it still can't find it, we're on unity 6.1.14f1

Start at DynamicCompilationBase.cs:66 and reproduce the crash in Unity 6.1.14f1. Inspect the AssetDatabase.FindAssets lookup and the reported package location for Microsoft.CSharp.dll. Done means the assembly is found without a Sequence contains no matching element crash when FastScriptReload runs.

Vom Indexierungsmodell aus dem Issue-Text verfasst.