Fix read more

[jmattheis]

To reproduce, create messages with varying height with and without images.

$ echo '\n\na\n\na\n\na\n\na\n\na\n\na\n\na\n\na\n\na![](https://placehold.co/650x452)' | gotify push --url 'http://localhost:8080' --token 'A.S0nAhucR2JCBN' --contentType text/markdown
$ echo '\n\na\n\na\n\na\n\na\n\na\n\na\n\na\n\na\n\na' | gotify push --url 'http://localhost:8080' --token 'A.S0nAhucR2JCBN' --contentType text/markdown
$ echo '\n\na\n\na\n\na\n\na\n\na\n\na\n\na\n\na\n\na\n\na\n\na\n\na\n\na\n\na\n\na\n\na\n\na\n\na\n\na\n\na\n\na\n\na\n\na\n\na\n\na\n\na\n\na\n\na\n\na\n\na\n\na\n\na\n\na\n\na\n\na\n\na' | gotify push --url 'http://localhost:8080' --token 'A.S0nAhucR2JCBN' --contentType text/markdown

@eternal-flame-AD, could you give this a try?

Fixes #846

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 78.77%. Comparing base (4329e57) to head (9ff713c).

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #848   +/-   ##
=======================================
  Coverage   78.77%   78.77%           
=======================================
  Files          56       56           
  Lines        2671     2671           
=======================================
  Hits         2104     2104           
  Misses        476      476           
  Partials       91       91           

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[eternal-flame-AD]

lgtm