test(igx-calendar): fix failing test, #6471

Author: wnvko

projects/igniteui-angular/src/lib/calendar/calendar-base.ts

@@ -620,7 +620,7 @@ export class IgxCalendarBaseDirective implements ControlValueAccessor {
      * Deselects date(s) (based on the selection type).
      */
     public deselectDate(value?: Date | Date[]) {
-        if (this.selectedDates || this.selectedDates.length === 0) {
+        if (!this.selectedDates || this.selectedDates.length === 0) {
             return;
         }