SF bug 567538: Generator can crash the interpreter (Finn Bock).

This was a simple typo.  Strange that the compiler didn't catch it!
Instead of WHY_CONTINUE, two tests used CONTINUE_LOOP, which isn't a
why_code at all, but an opcode; but even though 'why' is declared as
an enum, comparing it to an int is apparently not even worth a
warning -- not in gcc, and not in VC++. :-(