Fixes changing continuous mode while on tabs issue

Toggling the Continuous mode while opening multiple tabs caused an issue
in Okular, in which it considered it a global setting. So, toggling it
for one document, then toggling it again for the other documents may not
take effect. This should fix it by considering this setting a per
document setting, and therefore toggling the mode for one document
shouldn't have any effect for other documents.

BUGS: 422080