[Bugfix] Do not Crash when CHANGELOG would be Empty

[kevinmatthes]

No description provided.

[github-actions]

Filename                            Stmts    Miss  Cover    Missing
--------------------------------  -------  ------  -------  ----------------------------------------------
src/changelog/fragment.rs              88      55  37.50%   25, 102-182
src/changelog/ronlog.rs               203     138  32.02%   28-267, 333
src/changelog/comment_changes.rs      268     268  0.00%    26-449
src/version.rs                         69       0  100.00%
src/main.rs                             3       3  0.00%    22-24
src/macros.rs                          18       0  100.00%
src/complain.rs                       174      17  90.23%   29-70, 298, 302, 306, 310, 314, 318, 322
src/increment_version.rs              152      22  85.53%   32-48, 123-125, 144, 150-155, 234-235, 251-260
src/running.rs                          8       0  100.00%
src/cffreference.rs                   104       0  100.00%
src/application.rs                     64      64  0.00%    32-186
src/pattern/writer.rs                 125      51  59.20%   134-139, 146-154, 188-200, 232-262
src/pattern/buffer.rs                  33       0  100.00%
src/pattern/io_processor.rs            56      56  0.00%    73-162
src/traits/colour_message.rs           19       0  100.00%
src/traits/read_file.rs                56      39  30.36%   54-56, 69-71, 77-100, 105, 112-123, 133-146
src/traits/to_stderr.rs                 6       0  100.00%
src/traits/append_as_line.rs           12       0  100.00%
src/traits/file_formats.rs             25       0  100.00%
src/traits/convert_buffer.rs           30       0  100.00%
src/traits/prefer.rs                    5       0  100.00%
src/graphing/graph.rs                 219       3  98.63%   27, 109, 343
src/graphing/agd.rs                   228       2  99.12%   355, 377
TOTAL                                1965     718  63.46%