Stopwords behave incorrectly with ngram about manticoresearch

[sanikolaev]

MRE

echo ab > /tmp/stops; 
mysql -P9306 -h0 -v -e "drop table if exists t; create table t(f text) charset_table='c' stopwords='/tmp/stops' ngram_len='1' ngram_chars='a,b'; insert into t(f) values('a'); select * from t where match('a');"

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drop table if exists t
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create table t(f text) charset_table='c' stopwords='/tmp/stops' ngram_len='1' ngram_chars='a,b'
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insert into t(f) values('a')
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select * from t where match('a')
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Expected: the doc is found since there's the ab stopword, not a.