Fix running latex cell with cell marker

[DonJayamanne]

Fixes #10531

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 71%. Comparing base (e09de76) to head (23a1e29).
Report is 1796 commits behind head on main.

Additional details and impacted files

@@          Coverage Diff           @@
##            main   #10556   +/-   ##
======================================
- Coverage     71%      71%   -1%     
======================================
  Files        472      472           
  Lines      27987    27993    +6     
  Branches    4689     4691    +2     
======================================
+ Hits       19919    19921    +2     
- Misses      6190     6191    +1     
- Partials    1878     1881    +3     

Files with missing lines	Coverage Δ
...ractive-window/editor-integration/codeGenerator.ts	91% <100%> (+<1%)	⬆️

... and 27 files with indirect coverage changes

[amunger]

ha, I was about to mention that this change was a good candidate for unit tests

[DonJayamanne]

Had to add an integration test as this was a bad break, basically as bad as not being able to run a cell.
To me this is a golden scenario, not being able to run latext cells in IW.