ash: [PARSER] Fix parsing of ${##1}

Upstream commit:

    Date: Thu, 4 Oct 2007 22:15:10 +0800
    [PARSER] Fix parsing of ${##1}

    Previously dash treated ${##1} as a length operation.  This patch fixes that.

    Test case:

        set -- a
        echo ${##1}OK

    Old result:

        1OK

    New result:

        OK

This was a real bug in ash (but not in hush).

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

shell/ash_test/ash-vars/param_expand_len.right

@@ -7,3 +7,6 @@ Make sure len parsing doesnt break arg count
 Testing len op
 4 3 2 1 0 0
 0 3 0
+Nothing:
+Nothing:
+One:1

shell/ash_test/ash-vars/param_expand_len.tests

@@ -15,3 +15,10 @@ unset e
 f=abc
 g=
 echo ${#e} ${#f} ${#g}
+
+set -- a
+# This must be interpreted as: $# ("1"), then remove trailing "1".
+# IOW: empty result.
+echo Nothing:${##1}
+echo Nothing:${#%1}
+echo One:${##x}