fix(explore): bugs in Custom SQL editor in filter popover

[kgabryje]

SUMMARY

Fixes 2 bugs:

• 'undefined undefined' when SQL query is empty and we switch to another clause
• Save button inactive until clause is switched

BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF

TEST PLAN

ADDITIONAL INFORMATION

• Has associated issue: [explore]filter custom SQL editor is broken, adding undefined clause  #12266
• Changes UI
• Requires DB Migration.
• Confirm DB Migration upgrade and downgrade tested.
• Introduces new feature or API
• Removes existing feature or API

CC: @villebro @junlincc @rusackas

[villebro]

LGTM!

[villebro]

@kgabryje there is a minor change to current behavior that requires updating a unit test. Check the frontend build error (I think it's fine to update the test):

[codecov-io]

Codecov Report

Merging #12278 (e114b45) into master (d4a854e) will decrease coverage by 4.36%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master   #12278      +/-   ##
==========================================
- Coverage   67.17%   62.81%   -4.37%     
==========================================
  Files        1002     1002              
  Lines       49231    49275      +44     
  Branches     5000     5006       +6     
==========================================
- Hits        33073    30950    -2123     
- Misses      16035    18123    +2088     
- Partials      123      202      +79     

Flag	Coverage Δ
cypress	?
javascript	61.22% <100.00%> (-0.04%)	⬇️
python	63.83% <ø> (-0.37%)	⬇️

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

Impacted Files	Coverage Δ
...components/AdhocFilterEditPopoverSqlTabContent.jsx	65.51% <ø> (-1.15%)	⬇️
superset-frontend/src/explore/AdhocFilter.js	93.24% <100.00%> (-4.10%)	⬇️
superset-frontend/src/explore/exploreUtils.js	58.59% <100.00%> (-8.30%)	⬇️
superset-frontend/src/SqlLab/App.jsx	0.00% <0.00%> (-100.00%)	⬇️
superset-frontend/src/explore/App.jsx	0.00% <0.00%> (-100.00%)	⬇️
superset-frontend/src/dashboard/App.jsx	0.00% <0.00%> (-100.00%)	⬇️
superset-frontend/src/setup/setupColors.js	0.00% <0.00%> (-100.00%)	⬇️
superset-frontend/src/chart/ChartContainer.jsx	0.00% <0.00%> (-100.00%)	⬇️
superset-frontend/src/explore/reducers/index.js	0.00% <0.00%> (-100.00%)	⬇️
...et-frontend/src/dashboard/containers/Dashboard.jsx	0.00% <0.00%> (-100.00%)	⬇️
... and 217 more

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