Gollum: Compare Revisions redirect to error message when Edit option is disabled

[DanSman]

Describe the bug

1545

I have also another question about the editing mode. I disabled it and I can't compare versions without having the edit mode set on true. Is it possible to compare different versions without having the edit mode activated? Should I do another issue about it? I don't wanna bother you so much :)

To Reproduce
Steps to reproduce the behavior:

1. Add :allow_editing => false, to your config.rb
2. Click on 'Page History'
3. Compare Revisions

Expected behavior
To see the different versions in comparison.

Version
Gollum 5.0.1
Running on: x86_64-linux with Ruby version 2.7.1
Using:
rugged 0.99.0
gollum-rugged_adapter 0.99.4
gollum-lib 5.0.3
Markdown rendering gem: github/markdown
Other renderering gems:
none

[dometto]

The problem is here, coupled with the fact that the History view is POSTing the revision data to the compare view. Not sure what the best way to fix is. Would be a bit ugly to hardcode an exception for the compare view on L108. Also I don't see a super easy way to make the compare view use GET instead (although this is certainly possible).

[dometto]

Fixed in #1578 thanks to @tpoliaw! Many thanks