fix reference count on punned ColumnFamily Arc

Signed-off-by: Jason Volk <jason@zemos.net>

src/database/map.rs

@@ -233,7 +233,7 @@ fn open(db: &Arc<Engine>, name: &str) -> Result<Arc<ColumnFamily>> {
 	// closing the database (dropping `Engine`). Since `Arc<Engine>` is a sibling
 	// member along with this handle in `Map`, that is prevented.
 	Ok(unsafe {
-		Arc::decrement_strong_count(cf_ptr);
+		Arc::increment_strong_count(cf_ptr);
 		Arc::from_raw(cf_ptr)
 	})
 }