Extension not activated when opened solution not having any opened documents

[LuckyTil]

Versions

• Git Diff Margin version: 3.12.1
• Visual Studio version: 16.10.4

What happened

Extension not activated when opened solution not having any opened documents.

Steps to Reproduce

1. Start VS
2. Open solution.
3. Close All Tabs
4. Shutdown VS
5. Start VS
6. Open same solution
7. Open any source file
8. Start typing
9. --- Git Diff not react ---
10. Undo changes
11. Shutdown VS
12. Start VS
13. Open same solution
14. --- Source file Tab reopens ---
15. Start typing
16. --- Git Diff react now! ---