Restore BC in all() methods with empty Redmine response

[Art4]

This PR handles a possible bug of Redmine. If Redmine is called with an unknown query_id parameter, Redmine responses with an 404 status code and an empty response body.

I'm not sure if in this case we should return an empty array or throw an more meaningful exception. Because this case throws a JsonException at the moment, it should not be a breaking change to throw another exception.

Any thoughts?

Refs #335.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (a1fd6dd) 95.98% compared to head (5dbecd0) 96.37%.

Additional details and impacted files

@@             Coverage Diff              @@
##               v2.x     #337      +/-   ##
============================================
+ Coverage     95.98%   96.37%   +0.39%     
- Complexity      395      434      +39     
============================================
  Files            27       27              
  Lines          1220     1298      +78     
============================================
+ Hits           1171     1251      +80     
+ Misses           49       47       -2     

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[Art4]

I've investigated the issue about handling empty response bodies from Redmine and I've found a BC break in PHP-Redmine-API starting with v2.2.0 in AbstractApi::retrieveAll(). It turns out that this method was able to return array|false|string, but only array|false was documented in the PHPDoc tag.

After rewriting to AbstractApi::retrieveData() it only returns array or throws an exception. (That's the new and preferred way.) I will document this behavior in the new list() and listByX() methods, that are using the new retrieveData() method.

But for the (deprecated) AbstractApi::retrieveAll() and the (deprecated) all() methods I will restore the old behavior, so we should have BC again.