fix(sqllab): unable to create new tabs

[justinpark]

SUMMARY

The queryEditor's name can be undefined during localStorage hydration.
This commit skips the mappedUntitled case rather than throwing an error for this case.

BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF

TESTING INSTRUCTIONS

N/A

ADDITIONAL INFORMATION

• Has associated issue:
• Required feature flags:
• Changes UI
• Includes DB Migration (follow approval process in SIP-59)
  • Migration is atomic, supports rollback & is backwards-compatible
  • Confirm DB migration upgrade and downgrade tested
  • Runtime estimates and downtime expectations provided
• Introduces new feature or API
• Removes existing feature or API

[codecov]

Codecov Report

Merging #21260 (1b2b0d1) into master (05354a9) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master   #21260   +/-   ##
=======================================
  Coverage   66.43%   66.43%           
=======================================
  Files        1784     1784           
  Lines       68185    68185           
  Branches     7265     7265           
=======================================
  Hits        45298    45298           
  Misses      21018    21018           
  Partials     1869     1869           

Flag	Coverage Δ
javascript	52.49% <100.00%> (ø)

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

Impacted Files	Coverage Δ
...erset-frontend/src/SqlLab/utils/newQueryTabName.ts	86.66% <100.00%> (ø)

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