Fix inconsistencies in the preference names used by PDFViewerApplication

Since `preferenceSidebarViewOnLoad` is an enumeration value, it seems better to initialize it with the default one instead of a boolean.
`preferencesPdfBugEnabled` uses a superfluous "s", which is a typo I made when I introduced it.
Disables streaming in the extension when length is undefined.
Merge pull request #5373 from yurydelendik/issue5372

Disables streaming in the extension when length is undefined.
Merge pull request #5369 from Snuffleupagus/viewer-temp-pref-names

Fix inconsistencies in the preference names used by PDFViewerApplication