fix: If a "panel summary widget" is incomplete, the app shouldn't crash

[g123k]

Hi everyone,

This is a fix for #4948, but I won't link to the issue, as I'm not fully sure if it answers correctly the problem for the final user.
But basically this PR ensures the product page won't crash when there is no titleElement.
I have also improved a bit the code to only use a Column when there is at least 2 children.

[codecov-commenter]

Codecov Report

Attention: 5 lines in your changes are missing coverage. Please review.

Comparison is base (014557e) 9.61% compared to head (5fee0b8) 9.61%.

Files	Patch %	Lines
...s/smooth_app/lib/helpers/product_cards_helper.dart	0.00%	4 Missing ⚠️
...e_panel/knowledge_panels/knowledge_panel_card.dart	0.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           develop   #4987   +/-   ##
=======================================
  Coverage     9.61%   9.61%           
=======================================
  Files          323     323           
  Lines        16279   16279           
=======================================
  Hits          1565    1565           
  Misses       14714   14714           

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