chore: ensure flushed clipboard in spongev2 writer

worldedit-core/src/main/java/com/sk89q/worldedit/extent/clipboard/io/sponge/SpongeSchematicV3Writer.java

@@ -74,6 +74,10 @@ public class SpongeSchematicV3Writer implements ClipboardWriter {
 
     @Override
     public void write(Clipboard clipboard) throws IOException {
+        //FAWE start - ensure clipboard is flushed in case of using clipboard-on-disk. Maintains allowing of the same code
+        // between upstream and FAWE
+        clipboard.flush();
+        //FAWE end
         // For now always write the latest version. Maybe provide support for earlier if more appear.
         outputStream.writeNamedTag("",
             new CompoundTag(ImmutableMap.of("Schematic", new CompoundTag(write3(clipboard))))