handle empty each blocks

[Rich-Harris]

Addendum to #1292. Edge case, but currently causes an error

[codecov-io]

Codecov Report

Merging #1295 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #1295      +/-   ##
==========================================
+ Coverage   91.66%   91.66%   +<.01%     
==========================================
  Files         122      122              
  Lines        4329     4330       +1     
  Branches     1365     1366       +1     
==========================================
+ Hits         3968     3969       +1     
  Misses        148      148              
  Partials      213      213

Impacted Files	Coverage Δ
src/generators/nodes/EachBlock.ts	97.63% <100%> (+0.01%)	⬆️

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