ash: shrink by folding an if check into setprompt; unindent big block

ash: shrink by folding an if check into setprompt; unindent big block

function                                             old     new   delta
setprompt_if                                           -      66     +66
parseheredoc                                         126     124      -2
parsecmd                                              68      66      -2
redirect                                            1254    1249      -5
xxreadtoken                                          351     343      -8
readtoken1                                          3219    3204     -15
setprompt                                             62       -     -62
------------------------------------------------------------------------------
(add/remove: 1/1 grow/shrink: 0/5 up/down: 66/-94)            Total: -28 bytes

Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>