ash: parser: Fix handling of empty aliases

Upstream commit:

    Date: Tue, 28 Apr 2020 01:15:26 +1000
    parser: Fix handling of empty aliases

    Dash was incorrectly handling empty aliases. When attempting to use an
    empty alias with nothing else, I'm (incorrectly) prompted for more
    input:

    ```
    $ alias empty=''
    $ empty
    >
    ```

    Other shells (e.g., bash, yash) correctly handle the lone, empty alias as an
    empty command:

    ```
    $ alias empty=''
    $ empty
    $
    ```

    The problem here is that we incorrectly enter the loop eating TNLs
    in readtoken().  This patch fixes it by setting checkkwd correctly.

function                                             old     new   delta
list                                                 351     355      +4

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