Fix a problem when using the left key to change the ring and checkbox menu

items. The old code used modulus which does not give the required result,
for C (ISO 1990) and before the result is implementation defined so may have
worked for some compilers / targets but from C (ISO 1999) onwards the sign
of the result comes from the dividend so will not work. (By M. T. Jones)

ChangeLog

@@ -6,6 +6,7 @@ Key:
      * Something changed / fixed
 
 v0.5dev (ongoing development)
+ * Fix using the left key to change the ring and checkbox menu items
  * sed1520: Add an option for inverted segment mapping (idea by R. Buchert)
 
 v0.5.6

server/menu.c

@@ -734,18 +734,20 @@ MenuResult menu_process_input(Menu *menu, MenuToken token, const char *key, unsi
 			break;
 		switch (subitem->type) {
 		  case MENUITEM_CHECKBOX:
-			/* Note: this works as CheckboxValue is an enum >= 0. */
-			subitem->data.checkbox.value--;
-			subitem->data.checkbox.value %= (subitem->data.checkbox.allow_gray) ? 3 : 2;
+			if (subitem->data.checkbox.value == 0)
+				subitem->data.checkbox.value = (subitem->data.checkbox.allow_gray) ? 2 : 1;
+			else
+				subitem->data.checkbox.value--;
 
 			if (subitem->event_func)
 				subitem->event_func(subitem, MENUEVENT_UPDATE);
 			return MENURESULT_NONE;
 		  case MENUITEM_RING:
 			/* ring: jump to the end if beginning is reached */
-			/* Note: this works as data.ring.value is a short >= 0 */
-			subitem->data.ring.value--;
-			subitem->data.ring.value %= LL_Length(subitem->data.ring.strings);
+			if (subitem->data.ring.value == 0)
+				subitem->data.ring.value = LL_Length(subitem->data.ring.strings) - 1;
+			else
+				subitem->data.ring.value--;
 
 			if (subitem->event_func)
 				subitem->event_func(subitem, MENUEVENT_UPDATE);