ash: in dotrap(), do not clear gotsig[] for SIGINT if there is no handler

ash: in dotrap(), do not clear gotsig[] for SIGINT if there is no handler
 for it, otherwise raise interrupt gets confused later.
 The rest are readability fixes.

function                                             old     new   delta
evaltreenr                                           817     818      +1
evaltree                                             817     818      +1
evalstring                                            88      89      +1
cmdloop                                              420     419      -1
evalskip                                               4       1      -3
breakcmd                                              84      81      -3
ash_main                                            1382    1379      -3
evalloop                                             183     177      -6
evalfor                                              231     225      -6
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(add/remove: 0/0 grow/shrink: 3/6 up/down: 3/-22)             Total: -19 bytes