use cards, prevent negative servings

src/main.rs

@@ -75,7 +75,7 @@ async fn decrease(
         Path(id): Path<i32>
 ) -> Redirect{
     let conn = conn.lock().unwrap();
-    let mut stmt = conn.prepare("UPDATE food SET actual_servings = (SELECT actual_servings FROM food WHERE id = ?1) - 1 WHERE id = ?1").unwrap();
+    let mut stmt = conn.prepare("UPDATE food SET actual_servings = MAX((SELECT actual_servings FROM food WHERE id = ?1) - 1, 0) WHERE id = ?1").unwrap();
     stmt.execute((id,)).unwrap();
     Redirect::to("/")
 }