ash: eval: Restore input files in evalcommand

ash: eval: Restore input files in evalcommand

Upstream commit:

    Date: Tue, 27 Mar 2018 00:39:35 +0800
    eval: Restore input files in evalcommand

    When evalcommand invokes a command that modifies parsefile and
    then bails out without popping the file, we need to ensure the
    input file is restored so that the shell can continue to execute.

    Reported-by: Martijn Dekker <martijn@inlv.org>
    Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
function                                             old     new   delta
unwindfiles                                            -      20     +20
evalcommand                                         1635    1653     +18
getoptscmd                                           584     595     +11
popallfiles                                           20      10     -10
------------------------------------------------------------------------------
(add/remove: 1/0 grow/shrink: 2/1 up/down: 49/-10)             Total: 39 bytes

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