Add warning for submitting multiple highlights

public/_locales/en/messages.json

@@ -656,6 +656,9 @@
         "message": "To submit segments with the category of \"{0}\", you must enable it in the options. You will be redirected to the options now.",
         "description": "Used when submitting segments to only let them select a certain category if they have it enabled in the options."
     },
+    "poiOnlyOneSegment": {
+        "message": "Warning: This type of segment can have a maximum of one active at a time. Submitting multiple will cause a random one to be shown."
+    },
     "youMustSelectACategory": {
         "message": "You must select a category for all segments you are submitting!"
     },

src/components/SponsorTimeEditComponent.tsx

@@ -279,6 +279,11 @@ class SponsorTimeEditComponent extends React.Component<SponsorTimeEditProps, Spo
         if (getCategoryActionType(event.target.value as Category) === CategoryActionType.POI) {
             this.setTimeTo(1, null);
             this.props.contentContainer().updateEditButtonsOnPlayer();
+
+            if (this.props.contentContainer().sponsorTimesSubmitting
+                    .some((segment, i) => segment.category === event.target.value && i !== this.props.index)) {
+                alert(chrome.i18n.getMessage("poiOnlyOneSegment"));
+            }
         }
         
         this.saveEditTimes();