Fix `HashTable` badly handling reference counts

When `HashTable` was told to replace an object with itself, it ended up
incrementing its reference count because of the legacy equality check
(previously `FreeSelf()` completely deallocated an object, so the check
was warranted).

sources/Data/Collections/HashTable.uc

@@ -394,7 +394,7 @@ public final function HashTable SetItem(
     if (value != none) {
         value.NewRef();
     }
-    if (oldEntry.value != none && newEntry.value != oldEntry.value) {
+    if (oldEntry.value != none) {
         oldEntry.value.FreeSelf();
     }
     hashTable[bucketIndex].entries[entryIndex] = newEntry;

sources/Data/Collections/Tests/TEST_HashTable.uc

@@ -26,6 +26,7 @@ var private array<MockItem> mockedItems;
 protected static function TESTS()
 {
     Test_GetSet();
+    Test_Rewrite();
     Test_HasKey();
     Test_GetKeys();
     Test_GetTextKeys();
@@ -89,6 +90,21 @@ protected static function Test_GetSet()
     TEST_ExpectNone(array.GetItem(__().text.FromString("Some random stuff")));
 }
 
+protected static function Test_Rewrite()
+{
+    local Text      textObject;
+    local HashTable array;
+
+    array = HashTable(__().memory.Allocate(class'HashTable'));
+    Context("Testing getters and setters for items of `HashTable`.");
+    Issue("`SetItem()` does not handle reference counts correctly when"
+        @ "replacing a value with itself.");
+    textObject = __().text.FromString("value");
+    array.SetItem(__().text.FromString("key"), textObject);
+    array.SetItem(__().text.FromString("key"), textObject);
+    TEST_ExpectTrue(textObject._getRefCount() == 2);
+}
+
 protected static function Test_HasKey()
 {
     local HashTable array;