Plugin crashes with big text files.

[HugoRoss]

Steps to reproduce:

• Create a text file containing all file paths of drive C: like this (in a command line):

DIR C:*.* /S /B >C:\Temp\DiskContent.txt

(it takes quite a while)

• Open "C:\Temp\DiskContent.txt" in Visual Studio

If "Indent Guides" is disabled, I easily searches my 2.2 million lines. If "Indent Guides" is enabled, the plugin crashes and the GUI becomes unresponsive.