Jelly: Fix find in page functionality

The KeyEvent parameter maybe null, state it in function declaration. Else leads to a crash when the feature is used.

Test:
- Open app, load a webpage.
- Use the "Find in page" from options menu.
- Enter a keyword into the search box, press search option on keyboard, app crashes

With this change, no crash is observed, and the searched terms are highlighted on the page.

Fixes: https://gitlab.com/LineageOS/issues/android/-/issues/2165
Change-Id: Iad453173fa1417deb01de0b85cad8876ed68ccb1