Fix 'prevent-element-src-loading' — thrown error if 'thisArg' is undefined

[AdamWr]

Steps to reproduce

1. Add this rule

example.org#%#//scriptlet('prevent-element-src-loading', 'script', 'TEST_WHATEVER_QWERTYU')

2. Go to - https://example.org/
3. In browser console run:

addEventListener('visibilitychange', () => {
    console.log('test');
});

Script should works correctly, but it throws error, because thisArg is undefined in this case.

Screenshots

It looks like that it's a new issue and it worked correctly in previous version (I mean in scriptlets library 1.6.x).

[AdamWr]

Probably related issue - AdguardTeam/AdguardFilters#138389
Video player is broken due to:

player.pl#%#//scriptlet('prevent-element-src-loading', 'script', '/assets/adverts_.js')

but it worked correctly with previous version.