Fix zoom scale issues

[kbengs]

Steps to reproduce the issue:

• Open a PDF and zoom to full page
• Select all + Cut
• Paste
  -> The pages will not receive a thumbnail. Thumbnail is rendered but update_thumbnail does not accept the page.

[codecov-commenter]

Codecov Report

Merging #564 (5e37030) into main (0f25b5e) will increase coverage by 0.01%.
The diff coverage is 60.00%.

@@            Coverage Diff             @@
##             main     #564      +/-   ##
==========================================
+ Coverage   72.47%   72.49%   +0.01%     
==========================================
  Files          10       10              
  Lines        2936     2934       -2     
==========================================
- Hits         2128     2127       -1     
+ Misses        808      807       -1     

Impacted Files	Coverage Δ
pdfarranger/pdfarranger.py	67.33% <60.00%> (+0.02%)	⬆️

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[kbengs]

To reproduce second issue:

• Open a PDF
• Make window height as small as possible
• Zoom to full page
• Select all + cut
• Paste
  -> cairo.Error: invalid value.