fix grind modification

src/entity/item/weapon.rs

@@ -1513,7 +1513,7 @@ impl Weapon {
                         attr
                     });
                 }
-                self.grind += grind;
+                self.grind = std::cmp::max(self.grind as i32 + grind, 0) as u8;
                 self.tekked = true;
             },
             _ => {}