fix parse eval on SW_ARG2 caclulate r->rlen error

[kukey]

Problem

This bug is very hidden and must be reproduced using carefully constructed commands.
The key point is：

• the command is eval
• first enter parse SW_ARG2 (m = p + r->rlen) >= b->last

eg(mbuf is 512):
eval "return                                                                                                                                                                                                                                                                                                                                                                                                           {KEYS[1],KEYS[2],ARGV[1],ARGV[2]}   " 2 key1 first

Solution
When m > b->last will due to repair mbuf, so only r->token == NULL, need caculate r->rlen again.

Result