RRule: sanitize byday/month before using.

It was crashing when they were not array, so this change makes sure they are.
Additionally, since we don't support the number prefixes for by day (e.g.
3SA) at least sanitize the ones we can handle which are the ones
prefixed by 1 such as 1SA, and turn them into the equivalent SA.

src/widgets/RRule.tsx

@@ -83,6 +83,30 @@ const menuItemsWeekDays = weekdays.map((day) => {
   );
 });
 
+function makeArray<T>(item: T) {
+  if (item === undefined) {
+    return item;
+  } else if (Array.isArray(item)) {
+    return item;
+  } else {
+    return [item];
+  }
+}
+
+function sanitizeByDay(item: string | string[] | undefined) {
+  const ret = makeArray(item);
+  if (Array.isArray(ret)) {
+    return (ret as string[]).map((value) => {
+      if (parseInt(value) === 1) {
+        return value.substr(1);
+      }
+      return value;
+    });
+  } else {
+    return ret;
+  }
+}
+
 const styles = {
   multiSelect: { minWidth: 120, maxWidth: '100%' },
   width: { width: 120 },
@@ -152,7 +176,7 @@ export default function RRule(props: PropsType) {
           <FormControl>
             <InputLabel>Weekdays</InputLabel>
             <Select
-              value={options.byday ? options.byday : []}
+              value={sanitizeByDay(options.byday)}
               multiple
               style={styles.multiSelect}
               onChange={(event: React.ChangeEvent<{ value: unknown }>) => {
@@ -221,7 +245,7 @@ export default function RRule(props: PropsType) {
               <InputLabel>Months</InputLabel>
               <Select
                 style={styles.multiSelect}
-                value={options.bymonth ? options.bymonth : []}
+                value={makeArray(options.bymonth)}
                 multiple
                 onChange={(event: React.ChangeEvent<{ value: unknown }>) => {
                   const value = event.target.value as string[];