bug#72381: srfi-64: test-result-remove fails to remove property

Hello,

I think I found a bug in (srfi srfi-64) module shipped with GNU Guile.

When I try to remove a property from the result alist using this code:

    (use-modules (srfi srfi-64))
    (let ((r (test-runner-null)))
      (test-result-set! r 'arstars 'a)
      (test-result-remove r 'arstars))

I get the following error:

    Backtrace:
    In ice-9/boot-9.scm:
      1752:10  8 (with-exception-handler _ _ #:unwind? _ #:unwind-for-type _)
    In unknown file:
               7 (apply-smob/0 #<thunk 7f0fcff80300>)
    In ice-9/boot-9.scm:
        724:2  6 (call-with-prompt _ _ #<procedure default-prompt-handler (k proc)>)
    In ice-9/eval.scm:
        619:8  5 (_ #(#(#<directory (guile-user) 7f0fcff83c80>)))
    In ice-9/boot-9.scm:
       2836:4  4 (save-module-excursion _)
      4388:12  3 (_)
    In srfi/srfi-64/testing.scm:
       546:35  2 (test-result-remove #<test-runner pass-count: 0 fail-count: 0 xpass-count: 0…> …)
       548:55  1 (loop ((arstars . a)))
       548:47  0 (loop ())

    srfi/srfi-64/testing.scm:548:47: In procedure loop:
    In procedure car: Wrong type argument in position 1 (expecting pair): ()

From cursory look at the `test-result-remove' source, is seems that the named
let `loop' is missing a stop condition?

Have a nice day
Tomas Volf