stop the eliding of void $pkg_var from assert fail

stop the eliding of void $pkg_var from assert fail

The code to eliminate things like our($foo); from the runtime op_next
chain in rpeep() caused the oldoldop, oldop, o vars not to form a chain of
3 adjacent ops. Instead, oldoldop and oldop ended up equal, which later
caused an assertion failure in the padrange code for something like

    my($a,$b),$x,my($c,$d);