Using "find" will slow/freeze/crash gtranslator when the po file is big

STEP:

• open gtranslator
• open a big po file like gimp.po-ui.master.zh_CN.po
• use "find" to search some Chinese words like “蒙板” （English words can trigger this bug as well but better than Chinese words)
• click "find next" button repeatedly
• click "find next" button quickly and repeatedly if gtranslator didn't freeze or crash

RUNTIME:

• OS: Fedora Silverblue 39.20231125.0 (2023-11-25T02:15:38Z)
• DE: GNOME 45.1
• gtranslator: 45.3 from flathub

PS: #144 (closed) still exists.