D8385: Set the columns in "Overview" mode to match the amount of pages if document is small

[Lex Dem]

lexdem edited the summary of this revision.

REPOSITORY
  R223 Okular

REVISION DETAIL
  https://phabricator.kde.org/D8385

To: lexdem, #okular
Cc: ltoscano, aacid, rkflx, ngraham