ash: simplify "you have mail" code

ash: simplify "you have mail" code

function                                             old     new   delta
mailtime_hash                                          -       4      +4
redirect                                            1282    1280      -2
mailtime                                              40       -     -40
cmdloop                                              429     378     -51
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(add/remove: 1/1 grow/shrink: 0/2 up/down: 4/-93)             Total: -89 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>