T13518 isset private property

[niden]

Hello!

• Type: bug fix
• Link to issue: Phalcon\Mvc\Model::__isset doesn't account for the PHP empty failover #13518 [Bug] Result of empty construction on model properties #13900

In raising this pull request, I confirm the following:

• I have read and understood the Contributing Guidelines
• I have checked that another pull request for this purpose does not exist
• I wrote some tests for this PR
• I have updated the relevant CHANGELOG
• I have created a PR for the documentation about this change

Fixed Phalcon\Mvc\Model::__isset to take into account non visible properties by checking the getter if it exists
Fixed Phalcon\Mvc\Model::__set to return a more informative message if we are tying to access a non visible property

Thanks

[codecov]

Codecov Report

Merging #14659 into 4.1.x will increase coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##            4.1.x   #14659      +/-   ##
==========================================
+ Coverage   67.47%   67.49%   +0.01%     
==========================================
  Files         483      483              
  Lines      111391   111403      +12     
==========================================
+ Hits        75166    75192      +26     
+ Misses      36225    36211      -14

[ruudboon]

@niden I think we can sent this to 4.0.x branch

[niden]

Merging here and cherry picking to 4.0.1