Remove duplicate empty script labels in dropdown

CHANGELOG.md

@@ -22,6 +22,7 @@ The **"Breaking Changes"** listed below are changes that have been made in the d
 - Fix the map border not updating when a tileset is changed.
 - Improve the poor speed of the API functions `setMetatileTile` and `setMetatileTiles`.
 - Stop the Tileset Editor from scrolling to the initially selected metatile when saving.
+- Fix `0x0`/`NULL` appearing more than once in the scripts dropdown.
 - Fix the selection outline sticking in single-tile mode on the Prefab tab.
 
 ## [5.1.1] - 2023-02-20

src/core/map.cpp

@@ -479,9 +479,9 @@ QStringList Map::eventScriptLabels(Event::Group group) const {
     }
 
     scriptLabels.removeAll("");
-    scriptLabels.removeDuplicates();
     scriptLabels.prepend("0x0");
     scriptLabels.prepend("NULL");
+    scriptLabels.removeDuplicates();
 
     return scriptLabels;
 }