ash: [PARSER] Catch variable length expansions on non-existant specials

ash: [PARSER] Catch variable length expansions on non-existant specials

Upstream commit:

    Date: Thu, 30 Oct 2014 11:53:35 +0800
    [PARSER] Catch variable length expansions on non-existant specials

    Currently we only check special variable names that follow directly
    after $ or ${.  So errors such as ${#&} are not caught.  This patch
    fixes that by moving the is_special check to just before we print out
    the special variable name.

    Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
function                                             old     new   delta
readtoken1                                          2630    2635      +5

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