Add process to skip translation of empty cells

[ttsukagoshi]

Fix #74

[github-actions]

Coverage report

St.❔	Category	Percentage	Covered / Total
🔴	Statements	56.1% (-0.38% 🔻)	253/451
🟢	Branches	100%	26/26
🟡	Functions	66.67%	8/12
🔴	Lines	56.1% (-0.38% 🔻)	253/451

Show files with reduced coverage 🔻

St.❔	File	Statements	Branches	Functions	Lines
🔴	sheetsl.ts	56.1% (-0.38% 🔻)	100%	66.67%	56.1% (-0.38% 🔻)

Test suite run success

16 tests passing in 6 suites.

Report generated by 🧪jest coverage report action from 4635769