BUG #15921: invalid regular expression while parsing hunspell affix

The following bug has been logged on the website:

Bug reference: 15921
Logged by: Mike Minaev
Email address: minaev(dot)mike(at)gmail(dot)com
PostgreSQL version: 10.5
Operating system: Ubuntu 18.04
Description:

We are using this dictionary
https://github.com/postgrespro/hunspell_dicts/tree/master/hunspell_ru_ru_aot
for fts. But sometimes my request fails with error
ERROR: invalid regular expression: operation cancelled
CONTEXT: line 48 of configuration file
"/usr/share/postgresql/10/tsearch_data/ru_ru_aot.affix": "PFX 9 0 без ^[и]
"

I log such requests in my application, but i can't reproduce this problem on
my localhost. Seems problem appears while dictionary read from disk. What i
can to do to fix this problem?