Added fix for another potential multithreaded case for cache.

Case: consecutive gets.

src/main/java/ca/recrown/islandsurvivalcraft/caching/Cache.java

@@ -31,6 +31,7 @@ public class Cache<K, V> {
         } else {
             lock.lock();
             try {
+                if (data.containsKey(key)) return;
                 CacheValue<K, V> val = new CacheValue<>();
                 val.key = key;
                 val.value = value;

src/main/java/ca/recrown/islandsurvivalcraft/caching/CacheUsageStack.java

@@ -8,6 +8,7 @@ class CacheUsageStack<K, V> {
     private final ReentrantLock lock = new ReentrantLock();
 
     private void addValueToStackTop(CacheValue<K, V> value) {
+        if (value == first) return;
         if (first != null) {
             first.front = value;
             value.back = first;
@@ -91,6 +92,7 @@ class CacheUsageStack<K, V> {
         } finally {
             lock.unlock();
         }
+        size = 0;
     }
 
     public int size() {