Broken case-insensitive search for Cyrillic characters

[detouched]

Lapce Version

v0.3.1

System information

OS: macOS 14.4.0
Memory: 32 GiB
Architecture: x86_64

Describe the bug

When searching for a substring with Cyrillic characters with disabled Match case option, if the first character is uppercase, then no matches are found (even exact match isn't).

Example:

ПРИВЕТ
привет
Привет
HELLO
hello
Hello

If you search for hello, HELLO or hELLO, all three last rows match as expected. However, only привет matches the first three rows, whereas ПРИВЕТ and Привет surprisingly match no rows at all. In fact, as long as the first letter is lower case, the match works as expected, e.g. пРИВЕТ matches first three rows just fine.

Additional information

Interestingly, when Match case option is switched on, lookup works as expected.