heaven: Prevent integer underflow when player reaches max hours

When the player reaches 30 hours, we're currently getting a panic in
debug mode and an unhandled interger underflow in release mode.
Sidestep this by not performing the subtraction if the player has gained
enough hours.

src/states/heaven.rs

@@ -30,9 +30,15 @@ impl HeavenState {
         utils::get_element_by_id::<web_sys::Element>("heaven-collected-hours")
             .unwrap()
             .set_inner_html(&format!("{}", player.collected_hours));
-        utils::get_element_by_id::<web_sys::Element>("heaven-needed-hours")
-            .unwrap()
-            .set_inner_html(&format!("{}", 30 - player.collected_hours));
+        if player.collected_hours < 30 {
+            utils::get_element_by_id::<web_sys::Element>("heaven-needed-hours")
+                .unwrap()
+                .set_inner_html(&format!("{}", 30 - player.collected_hours));
+        } else {
+            utils::get_element_by_id::<web_sys::Element>("heaven-needed-hours")
+                .unwrap()
+                .set_inner_html("None!");
+        }
 
         // Assign a random shift
         let assigned_shift = angel_shifts::generate_random_shift(&mut rand::thread_rng());