fix: correct null check for condition threshold to allow 0 values

[riahk]

SUMMARY

• Add an extra !== undefined check to condition threshold to allow falsey values (0) to display in edit mode

BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF

TEST PLAN

Manual test:

1. Create an alert with condition threshold of 0
2. Save
3. Edit same alert and ensure that threshold displays properly

ADDITIONAL INFORMATION

• Has associated issue:
• Changes UI
• Requires DB Migration.
• Confirm DB Migration upgrade and downgrade tested.
• Introduces new feature or API
• Removes existing feature or API

[codecov-io]

Codecov Report

Merging #12295 (0d77b28) into master (4149ab4) will decrease coverage by 15.76%.
The diff coverage is 0.00%.

@@             Coverage Diff             @@
##           master   #12295       +/-   ##
===========================================
- Coverage   67.17%   51.40%   -15.77%     
===========================================
  Files        1002      466      -536     
  Lines       49232    16760    -32472     
  Branches     5000     4303      -697     
===========================================
- Hits        33073     8616    -24457     
+ Misses      16036     8144     -7892     
+ Partials      123        0      -123     

Flag	Coverage Δ
cypress	51.40% <0.00%> (-0.01%)	⬇️
javascript	?
python	?

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
...frontend/src/views/CRUD/alert/AlertReportModal.tsx	4.41% <0.00%> (-41.99%)	⬇️
...uperset-frontend/src/dashboard/util/dnd-reorder.js	0.00% <0.00%> (-100.00%)	⬇️
...rset-frontend/src/dashboard/util/getEmptyLayout.js	0.00% <0.00%> (-100.00%)	⬇️
...dashboard/components/resizable/ResizableHandle.jsx	0.00% <0.00%> (-100.00%)	⬇️
.../src/dashboard/util/getFilterScopeFromNodesTree.js	0.00% <0.00%> (-93.48%)	⬇️
...set-frontend/src/views/CRUD/alert/ExecutionLog.tsx	11.76% <0.00%> (-88.24%)	⬇️
...src/dashboard/components/gridComponents/Header.jsx	10.52% <0.00%> (-86.85%)	⬇️
superset-frontend/src/components/IconTooltip.tsx	13.33% <0.00%> (-86.67%)	⬇️
...rc/dashboard/components/gridComponents/Divider.jsx	13.33% <0.00%> (-86.67%)	⬇️
...end/src/SqlLab/components/ExploreResultsButton.jsx	8.00% <0.00%> (-84.00%)	⬇️
... and 857 more

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