Fix scrolling computation

[mfl28]

• Fixes division-by-zero case when computing scrolling hvalue and vvalue. This happens when the viewport and content pane sizes (doubles) are exactly equal. This seems to happen frequently in Ubuntu (22).
• Note: Testfx does not seem to allow reproducing the issue via tests.

Fixes #70 .

[codecov]

Codecov Report

Patch coverage: 75.00% and project coverage change: -0.03 ⚠️

Comparison is base (2d46fda) 85.75% compared to head (d310c0c) 85.72%.

Additional details and impacted files

@@             Coverage Diff              @@
##             master      #72      +/-   ##
============================================
- Coverage     85.75%   85.72%   -0.03%     
- Complexity     1409     1410       +1     
============================================
  Files            92       92              
  Lines          5763     5767       +4     
  Branches        522      524       +2     
============================================
+ Hits           4942     4944       +2     
- Misses          562      563       +1     
- Partials        259      260       +1     

Impacted Files	Coverage Δ
...fl28/boundingboxeditor/ui/EditorImagePaneView.java	85.43% <75.00%> (-0.57%)	⬇️

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[sonarcloud]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

75.0% Coverage
0.0% Duplication