call and match bypasses bounds check

[andrewchambers]

use std

const main = {
    var name
    var path = "/xxx"[:]

    match std.strfind(path, "/")
    | `std.Some i:
        name = path[0:i-1]
    | `std.None:
    ;;
    std.put("FAIL\n")
}

ac@black:~/Desktop/bug$ mbld -R bug.myr 
/tmp/runmyr1962868523...
    6m  bug.myr 
    ld  -o /tmp/runmyr1962868523 /usr/local/lib/myr/_myrrt.o bug.o -L/usr/local/lib/myr -lstd -lsys 
    /tmp/runmyr1962868523   
FAIL

[oridb]

This issue, I think, comes in 2 parts:

1. We are doing a signed check on the bounds, so upper, in this case, is less than lower.
2. We aren't checking that upper > lower.

We should probably do this, although I cringe a bit on the efficiency front. I guess if/when we get VRP going, this will become much less painful.