Fix colors behind errors in the Python Interactive window.

[rchiodo]

For #3175

Also make sure empty markdown doesn't cause a split.

• Pull request represents a single change (i.e. not fixing disparate/unrelated things in a single PR)
• Title summarizes what is changing
• Has a news entry file (remember to thank yourself!)
• Has sufficient logging.
• Has telemetry for enhancements.
• Unit tests & system/integration tests are added/updated
• Test plan is updated as appropriate
• package-lock.json has been regenerated by running npm install (if dependencies have changed)
• The wiki is updated with any design decisions/details.

[rchiodo]

I had a customer complain on the colorization issue that I fixed that colors still weren't working. That was because of this problem.

[codecov]

Codecov Report

Merging #4683 into master will increase coverage by 1%.
The diff coverage is 100%.

@@          Coverage Diff           @@
##           master   #4683   +/-   ##
======================================
+ Coverage      77%     77%   +1%     
======================================
  Files         447     447           
  Lines       21343   21345    +2     
  Branches     3491    3493    +2     
======================================
+ Hits        16344   16346    +2     
  Misses       4995    4995           
  Partials        4       4

Flag	Coverage Δ
#Linux	66% <67%> (+1%)	⬆️
#Windows	66% <67%> (ø)	⬇️
#macOS	65% <67%> (+1%)	⬆️

[IanMatthewHuff]