Fix recurrence rule expansion with ordered weekday

When the order of a weekday in BYDAY rule expansion (like -5SA or 5SU
for monthly or 55WE for yearly) exceeds the number of available weekdays
in the period (month or year), rule expansion with negative order could
result in a floating point exception. The reason: the modified frequency
might become zero.

Solution. Check order against number of available weekdays and terminate
expansion early whenever possible (also for positive orders).

Signed-off-by: Lars Henriksen <LarsHenriksen@get2net.dk>
Signed-off-by: Lukas Fleischer <lfleischer@calcurse.org>

test/data/rfc5545

@@ -25,3 +25,4 @@
 12/25/1997 [1] {3Y w-11} Last Thursday of the year every third year, forever (FREQ=YEARLY;INTERVAL=3;BYDAY=-1TH)
 06/22/1997 [1] {2Y w0 w1} Every Sunday and Monday, every other year (FREQ=YEARLY;INTERVAL=2;BYDAY=SU,MO)
 02/01/1997 [1] {1Y -> 01/31/2005 d1 d29 m2} Every year on February 1 and 29 for eight years (RRULE:FREQ=YEARLY;UNTIL=20050131T000000Z;BYMONTH=2;BYMONTHDAY=1,29)
+08/01/2020 @ 08:41 -> 08/01/2020 @ 10:11 {1M w-41} |negative ordered weekday may not exist

test/recur-009.sh

@@ -6,6 +6,13 @@
 if [ "$1" = 'actual' ]; then
   "$CALCURSE" --read-only -D "$DATA_DIR"/ -c "$DATA_DIR/rfc5545" \
   -Q --from 1/1/1996 --to 12/31/2007 --filter-type recur
+  echo ""
+  echo "Floating point exception?"
+  "$CALCURSE" --read-only -D "$DATA_DIR"/ -c "$DATA_DIR/rfc5545" \
+  -Q --day 8/1/2020 --filter-type recur &&
+  "$CALCURSE" --read-only -D "$DATA_DIR"/ -c "$DATA_DIR/rfc5545" \
+  -Q --day 11/1/2020 --filter-type recur &&
+  echo "No Floating point exception on November 1, 2020"
 elif [ "$1" = 'expected' ]; then
   cat <<EOD
 11/05/96:
@@ -5323,6 +5330,12 @@ elif [ "$1" = 'expected' ]; then
 
 12/31/07:
  * Every Sunday and Monday, every other year (FREQ=YEARLY;INTERVAL=2;BYDAY=SU,MO)
+
+Floating point exception?
+08/01/20:
+ - 08:41 -> 10:11
+	negative ordered weekday may not exist
+No Floating point exception on November 1, 2020
 EOD
 else
   ./run-test "$0"