Key a (best-fit) sometimes truncates the PDF view while a search is active

[vinc17fr]

When a search is active, key a (best-fit) sometimes truncates the PDF view.

Tested with zathura 0.5.8 under Debian/unstable.

To reproduce:

1. Open a PDF file (it can have only 1 page, but the issue is more visible with at least 2 pages), e.g. babel-bib.pdf as a small example.
2. Type - (the goal is to ensure that best-fit is not active yet).
3. Search for text that exists, e.g. with /e then [Enter] on the above example.
4. Open the window to its maximum size; the F11 key to switch to fullscreen mode also works.
5. Type a to use best-fit mode.

The result is that the document does not appear in best-fit mode, and the pages are truncated. The + and - keys also have a strange effect: they change the zoom of the background of the matches, but not the text itself.