Pass correct group sizes to "GroupedVirtuoso" (#537)

One item was always hidden from the list.
Noticed during searching for a specific extension, which caused the list to only have one item, which was not shown

Was incorrectly changed with db65b9d

src/screens/Extensions.tsx

@@ -135,7 +135,7 @@ export function Extensions() {
     );
 
     const groupCounts = useMemo(
-        () => filteredGroupedExtensions.map((extensionGroup) => extensionGroup[EXTENSIONS].length - 1),
+        () => filteredGroupedExtensions.map((extensionGroup) => extensionGroup[EXTENSIONS].length),
         [filteredGroupedExtensions],
     );
     const visibleExtensions = useMemo(