Fix for Mantis #17598. When extended syntax is off allow the result of constructors to be dropped when the constructor is called as an instance method instead of a class method.

pstatmnt.pas, statement:
  * check whether the constructor is called as an instance or class method
nflw.pas, tlabelnode.pass_1:
  * don't check the owner of the labelsym when there is none (happens with internally created labels like for e.g. exception handling)

+ added test  

git-svn-id: http://svn.freepascal.org/svn/fpc/trunk@25068 3ad0048d-3df7-0310-abae-a5850022a9f2