PhpStan fixes

[janbarasek]

• bug fix
• BC break? yes

Fixed PhpStan suggestions:

------ ------------------------------------------------------------------------ 
 Line   RobotLoader/RobotLoader.php                                             
------ ------------------------------------------------------------------------ 
 125    Call to function is_array() with string will always evaluate to false.  
 147    Call to function is_array() with string will always evaluate to false.  
 244    Parameter #2 $subject of function preg_split expects string, array      
        given.                                                                  
 255    Parameter #2 $subject of function preg_split expects string, array      
        given.                                                                  
 347    Variable $name might not be defined.                                    
 369    Variable $name might not be defined.                                    
 375    Variable $name might not be defined.                                    
------ ------------------------------------------------------------------------ 

[JanTvrdik]

I'm not sure it's a good idea to document deprecated APIs.

[dg]

Thanks. I'll merge it without documentation for deprecated API.