fix #13624 DemoConsole app: An exception pops up when focusing on "Type Here" in contextMenuStrip under DarkMode

[Epica3055]

Fix #13624

Proposed changes

• add null check like we did here

Before

Exception.mp4

After

no Exception

Test methodology

• manual test

Microsoft Reviewers: Open in CodeFlow

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 1 line in your changes missing coverage. Please review.

Project coverage is 76.60341%. Comparing base (08485db) to head (753da08).
Report is 1 commits behind head on main.

Additional details and impacted files

@@                 Coverage Diff                 @@
##                main      #13635         +/-   ##
===================================================
- Coverage   76.60828%   76.60341%   -0.00487%     
===================================================
  Files           3253        3253                 
  Lines         640996      640995          -1     
  Branches       47439       47439                 
===================================================
- Hits          491056      491024         -32     
- Misses        146290      146321         +31     
  Partials        3650        3650                 

Flag	Coverage Δ
Debug	76.60341% <0.00000%> (-0.00487%)	⬇️
integration	18.98972% <0.00000%> (-0.00413%)	⬇️
production	51.05805% <0.00000%> (-0.01096%)	⬇️
test	97.41175% <ø> (ø)
unit	48.43629% <0.00000%> (-0.01061%)	⬇️

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