Fix #1669 and #1670 - announcements no permission error and wrong $unvie...

...wablefids

Merged arrays with unviewable fids so that all are considered now:
https://github.com/mybb/mybb/issues/1669

And corrected variable in 2 conditionals to fix this:
https://github.com/mybb/mybb/issues/1670
Isn't there a possibility that the input to be already encoded?
https://github.com/mybb/mybb/pull/1671/files#diff-7a3b4fcc2232bedfda5a1642e3600675R3245