Don't loop forever if a reminder moves backwards because of a time zone difference.

If we are not making progress, it's because the reminder has expired.

tests/test-timezone-support

@@ -161,6 +161,9 @@ debug -t
 
 EOF
 
+TZ=America/Toronto $REMIND -s - 2025-09-01@00:00 <<'EOF' >> $OUT 2>&1
+REM 2025-09-24 AT 09:00 TZ America/Denver MSG Dr. Smith
+EOF
 cmp -s $OUT $CMP
 if [ "$?" = "0" ] ; then
     echo "Remind:   Time zone test PASSED"

tests/tz.cmp

@@ -78,3 +78,4 @@ trig("Mon at 00:00 TZ Australia/Sydney", "Tue at 00:00 TZ America/Toronto", "Wed
 -stdin-(14:21): Trig(tz_adj Australia/Sydney) = Saturday, 6 September, 2025 AT 10:00
 -stdin-(14:21): Trig = Monday, 1 September, 2025 AT 14:42
 2025-09-01
+2025/09/24 * * * 660 11:00am Dr. Smith