ime input at wrong position

[tkkcc]

run master (6e0eb6cd02924c6bb6d5159c3c61e4a05a6b0688) editor example, input text in the middle using ime, but it prepend to begin, not insert after cursor.

env: archlinux + fcitx5 5.1.10

but lapce 0.4.0.r139.g16ebd02-1 's extension search text input does't have this issue