Only consume potions if they have an effect

src/artifacts.rs

@@ -68,8 +68,11 @@ impl Artifact for Potion {
     }
     fn get_immutable_position(&self) -> &Position { &self.position }
     fn collect(&mut self, player: &mut Player) {
-        player.change_life(self.health.try_into().unwrap());
-        self.health = 0;
+        // only consume potion of the player can gain at least one health point
+        if !player.is_healthy() {
+            player.change_life(self.health.try_into().unwrap());
+            self.health = 0;
+        }
     }
 
     fn was_collected(&self) -> bool {

src/player.rs

@@ -28,11 +28,13 @@ impl Player {
     pub fn change_life(&mut self, by: i16) {
         self.life = max(0, min(self.max_life, self.life + by));
     }
-    /// returns true if the player is dead (life <= 0)
     pub fn get_life(&self) -> i16 {
         self.life
     }
+    /// returns true if the player is dead (life <= 0)
     pub fn is_dead(&self) -> bool { self.life <= 0 }
+    /// returns true if the player's life is at maximum
+    pub fn is_healthy(&self) -> bool { self.life == self.max_life }
     pub fn get_max_life(&self) -> i16 {
         self.max_life
     }