"Column to predict (Label)" not populated

**System Information (please complete the following information):**
- Model Builder Version (available in Manage Extensions dialog): 17.15.0.2337001
- Visual Studio Version: 17.10.1

**Describe the bug**
- On which step of the process did you run into an issue: I tried following the guide here https://dotnet.microsoft.com/en-us/learn/ml-dotnet/get-started-tutorial/data. Chose the yelp_labelled.txt file, "Data Preview" is populated.
- Clear description of the problem: The drop-down menu "Column to predict (Label)" only contains "Select column" and not "col0", "col1" as expected. Since I cannot select a column to predict, I can't continue to the next step in the guide.

**To Reproduce**
Steps to reproduce the behavior:
1. Follow the steps in https://dotnet.microsoft.com/en-us/learn/ml-dotnet/get-started-tutorial/data
2. Selecting "Column to predict (Label)" is not possible

**Expected behavior**
I expected the "Column to predict (Label)" to be populated with the items "col0" and "col1"

**Screenshots**

Inizia seguendo il tutorial sui dati collegato in Model Builder con yelp_labelled.txt e riproduci il menu vuoto "Column to predict (Label)" dopo il caricamento di Data Preview. Il lavoro è completato quando il menu contiene col0 e col1 e il workflow può procedere al passaggio successivo.

Scritto dal modello di indicizzazione a partire dal testo della issue.