Change the semantics of evaluating non-local returns for blocks not on stack

Do evaluate the expression unconditionally, think, this is the standard stack-machine semantics. And only on the actual return, check whether the block is on the stack.

This should be tested in the TestSuite... [TODO!]

Signed-off-by: Stefan Marr <git@stefan-marr.de>
Use direct return in all code paths, to simplify

Signed-off-by: Stefan Marr <git@stefan-marr.de>
Simplify loop condition

Signed-off-by: Stefan Marr <git@stefan-marr.de>
Whitespace

Signed-off-by: Stefan Marr <git@stefan-marr.de>