Exception during execution of AsyncTests.Imported_AsyncWithEH terminates test process

[sharwell]

The following method appears to be at fault for a TestHost crash in https://dev.azure.com/dnceng-public/public/_build/results?buildId=593505&view=ms.vss-test-web.build-test-results-tab&runId=14348754&resultId=165403&paneView=dotnet-dnceng.dnceng-build-release-tasks.helix-test-information-tab.

The crash dump indicates a NullReferenceException was thrown within an AsyncVoidMethodBuilder leading to a process crash.

roslyn/src/Compilers/VisualBasic/Test/Emit/CodeGen/CodeGenAsyncTests.vb

Lines 4630 to 4711 in 8c55b1f

	<Fact,
	WorkItem(94940, "https://devdiv.visualstudio.com/defaultcollection/DevDiv/_workitems#_a=edit&id=94940"),
	WorkItem(785170, "http://vstfdevdiv:8080/DevDiv2/DevDiv/_workitems/edit/785170")>
	Public Sub Imported_AsyncWithEH()
	CompileAndVerify(
	<compilation>
	<file name="a.vb">
	Imports System
	Imports System.Threading
	Imports System.Threading.Tasks
	Module Module1
	Dim awaitCount As Integer = 0
	Dim finallyCount As Integer = 0
	Sub LogAwait()
	awaitCount += 1
	End Sub
	Sub LogException()
	finallyCount += 1
	End Sub
	Public Async Sub F(handle As AutoResetEvent)
	Await Task.Factory.StartNew(AddressOf LogAwait)
	Try
	Await Task.Factory.StartNew(AddressOf LogAwait)
	Try
	Await Task.Factory.StartNew(AddressOf LogAwait)
	Try
	Await Task.Factory.StartNew(AddressOf LogAwait)
	Throw New Exception()
	Catch ex As Exception
	Finally
	LogException()
	End Try
	Await Task.Factory.StartNew(AddressOf LogAwait)
	Throw New Exception()
	Catch ex As Exception
	Finally
	LogException()
	End Try
	Await Task.Factory.StartNew(AddressOf LogAwait)
	Throw New Exception()
	Catch ex As Exception
	Finally
	LogException()
	End Try
	Await Task.Factory.StartNew(AddressOf LogAwait)
	handle.Set()
	End Sub
	Public Sub Main2(i As Integer)
	awaitCount = 0
	finallyCount = 0
	Dim handle As New AutoResetEvent(False)
	F(handle)
	Dim completed = handle.WaitOne(4000)
	If completed Then
	If Not (awaitCount = 7 And finallyCount = 3) Then
	Throw New Exception("failed at " &amp; i)
	End If
	Else
	Throw New Exception("did not complete in time: " &amp; i)
	End If
	End Sub
	Public Sub Main()
	For i As Integer = 0 To 2000
	Main2(i)
	Next
	End Sub
	End Module
	</file>
	</compilation>, useLatestFramework:=True, expectedOutput:="")
	End Sub