Changing conversion length affects preceding phrase conversion in some cases

**Description**
When I change the conversion length, it sometimes affects the conversion of the preceding phrase.

**Steps to reproduce**
Steps to reproduce the behavior:
1. かしごじゅうどだいなかば
2. 歌詞五重土台半ば
3. 華氏50土台半ば
4. Change the conversion length of "土台半ば"

**Expected behavior**
華氏50℃台半ば

**Actual behavior**
華氏五十℃台半ば

**Version or commit-id**
Mozc-2.28.5050.100+24.11.oss

**Environment**
- OS: Windows11

**Investigations**
- Whether this issue happens on other IMEs (e.g. Anthy, SKK).
+ no