TDBGridColumnsPropertyEditorForm: Clicking "Delete All" causes crash of IDE.

Original Reporter info from Mantis: FTurtle @FTurtle

• Reporter name:

Description:

See steps to reproduce.

Steps to reproduce:

1. Open project examples\database\dblookup\project1.lpi
   
2. Open Form1.
   
3. Double click on DBGrid1.
   
4. Click "Add Fields".
   
5. Click on any field for selecting, let it be MTH_NO
   
6. Click "Delete All", answer "Yes".
   
7. Try drag form on header.
   
8. Get hanging IDE with or without chain of exceptions.

Do everything exactly without anything else.
Tested under Windows.

Mantis conversion info:

• Mantis ID: 33000
• Build: 57015
• Version: 1.9 (SVN)
• Fixed in revision: r57042 (#bb2b8fea)
• Target version: 1.8.2