fix: handled thread not found result on frontend

[mehaknasir]

INF-669

Related Backend Change: openedx/edx-platform#31340

Focus on the IDs of the thread and course in the screenshot to understand the fix:

original course with thread

course trying to fetch a thread that does not belong to it

also handled for the edit use case

[codecov]

Codecov Report

Base: 85.19% // Head: 85.09% // Decreases project coverage by -0.10% ⚠️

Coverage data is based on head (ece0f4b) compared to base (5c3d561).
Patch coverage: 77.77% of modified lines in pull request are covered.

❗ Current head ece0f4b differs from pull request most recent head e685fb9. Consider uploading reports for the commit e685fb9 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #360      +/-   ##
==========================================
- Coverage   85.19%   85.09%   -0.11%     
==========================================
  Files         134      134              
  Lines        2675     2683       +8     
  Branches      737      742       +5     
==========================================
+ Hits         2279     2283       +4     
- Misses        374      378       +4     
  Partials       22       22              

Impacted Files	Coverage Δ
src/discussions/comments/messages.js	100.00% <ø> (ø)
src/discussions/posts/post-editor/messages.js	100.00% <ø> (ø)
src/discussions/posts/post-editor/PostEditor.jsx	85.14% <20.00%> (-2.61%)	⬇️
src/discussions/comments/CommentsView.jsx	95.08% <100.00%> (+0.34%)	⬆️
src/discussions/comments/comment/Comment.jsx	95.55% <100.00%> (+0.10%)	⬆️
src/discussions/posts/data/api.js	91.89% <100.00%> (ø)
src/discussions/posts/data/thunks.js	87.06% <100.00%> (-0.87%)	⬇️
src/discussions/posts/data/slices.js	79.23% <0.00%> (ø)

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