ash: parser: Fix single-quoted patterns in here-documents

Upstream commit:

    From: Herbert Xu <herbert@gondor.apana.org.au>
    Date: Fri, 9 Mar 2018 23:07:53 +0800
    parser: Fix single-quoted patterns in here-documents

    The script

            x=*
            cat <<- EOF
                    ${x#'*'}
            EOF

    prints * instead of nothing as it should.  The problem is that
    when we're in sqsyntax context in a here-document, we won't add
    CTLESC as we should.  This patch fixes it:

    Reported-by: Harald van Dijk <harald@gigawatt.nl>
    Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

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

shell/ash.c

@@ -12005,7 +12005,7 @@ readtoken1(int c, int syntax, char *eofmark, int striptabs)
 				}
 			}
 #endif
-			if (eofmark == NULL || synstack->dblquote)
+			if (!eofmark || synstack->dblquote || synstack->varnest)
 				USTPUTC(CTLESC, out);
 			USTPUTC(c, out);
 			break;