[fix] parse error with folded scalars that are the last in a container

[biojppm]

fixes #152

[codecov]

Codecov Report

Merging #157 (0c99390) into master (1daa5ca) will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #157      +/-   ##
==========================================
+ Coverage   95.95%   95.97%   +0.01%     
==========================================
  Files          63       63              
  Lines       11954    11997      +43     
==========================================
+ Hits        11471    11514      +43     
  Misses        483      483              

Impacted Files	Coverage Δ
src/c4/yml/parse.hpp	98.55% <ø> (ø)
src/c4/yml/parse.cpp	92.00% <100.00%> (+0.06%)	⬆️
test/test_block_folded.cpp	100.00% <100.00%> (ø)

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