Selecting empty csv file throws an Exception

System Information (please complete the following information):

• (No idea where I can get Model builder version)
• Visual studio version is 17.11.0 Preview 7.0

Describe the bug
When I select Question Answer template, and then select empty file it throws an Exception

To Reproduce
Steps to reproduce the behavior:
Create Machine learning model
Select a Question Answering template (Local)
Press next step
Browse
Select an empty csv file

Expected behavior
I would expect some message that the file is empty.

Error
Unable to parse file. Only comma, tab or semi-colon delimited files are allowed.

at StreamJsonRpc.JsonRpc.d__154`1.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at Microsoft.ML.ModelBuilder.Actions.DataTextActions.d__14.MoveNext() in //src/Microsoft.ML.ModelBuilder/Actions/DataTextActions.cs:line 284
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at Microsoft.ML.ModelBuilder.Actions.DataTextActions.d__2.MoveNext() in //src/Microsoft.ML.ModelBuilder/Actions/DataTextActions.cs:line 61
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at Microsoft.ML.ModelBuilder.ToolWindows.DataTextViewModel.d__136.MoveNext() in //src/Microsoft.ML.ModelBuilder/ViewModels/DataTextViewModel.cs:line 683
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at Microsoft.ML.ModelBuilder.ToolWindows.TextDataControl.<<BrowseFileButton_Click>b__3_0>d.MoveNext() in //src/Microsoft.ML.ModelBuilder/ToolWindows/DataTabComponents/TextDataControl.xaml.cs:line 69

Screenshots

从 Microsoft.ML.ModelBuilder/Actions/DataTextActions.cs 第284行附近开始，并跟踪调用到 ViewModels/DataTextViewModel.cs 第683行附近。使用空 CSV 重现 Question Answering 模板流程，然后验证它报告文件为空，而不是出现分隔符异常。