Add filter s/t timeslot in progress cannot be selected

src/main/java/nl/tudelft/ewi/queue/model/Lab.java

@@ -418,8 +418,9 @@ public class Lab implements Serializable {
     }
 
     public Boolean slotIsAvailable(RequestSlot slot) {
-        LocalDateTime twoMinutesGracePeriod = now().minusMinutes(2L);
-        if (slot.getOpensAt().isBefore(twoMinutesGracePeriod)) {
+        LocalDateTime now = now();
+        LocalDateTime twoMinutesGracePeriod = now.minusMinutes(2L);
+        if (slot.getOpensAt().isBefore(twoMinutesGracePeriod) || (slot.getOpensAt().isBefore(now) && slot.getClosesAt().isAfter(now))) {
             return false;
         }
         int numberOfRequestsOnSlot = getNumberOfRequestsOnSlot(slot);