Fix regression in FreeListRef where no memory was allocated for the r…

…ef count. Fixes #1432.

Commit 6be5471 switched FreeListRef to use FreeListObjectAlloc underneath, but didn't accound for the extra memory that is needed to store the reference count directly after the object payload. The possible implications of this are memory corruption and memory leaks, although with the predefined allocator setip, this will only happen to types with a POT size or slightly less.

This commit adds an "EXTRA" template type parameter to FreeListObjectAlloc that is used to determine the additional amount of allocated memory, which is set to "int" in the case of FreeListRef.

source/vibe/utils/memory.d

@@ -611,10 +611,10 @@ nothrow:
 	}
 }
 
-struct FreeListObjectAlloc(T, bool USE_GC = true, bool INIT = true)
+struct FreeListObjectAlloc(T, bool USE_GC = true, bool INIT = true, EXTRA = void)
 {
 	enum ElemSize = AllocSize!T;
-	enum ElemSlotSize = max(AllocSize!T, Slot.sizeof);
+	enum ElemSlotSize = max(AllocSize!T + AllocSize!EXTRA, Slot.sizeof);
 
 	static if( is(T == class) ){
 		alias TR = T;
@@ -675,7 +675,7 @@ template AllocSize(T)
 
 struct FreeListRef(T, bool INIT = true)
 {
-	alias ObjAlloc = FreeListObjectAlloc!(T, true, INIT);
+	alias ObjAlloc = FreeListObjectAlloc!(T, true, INIT, int);
 	enum ElemSize = AllocSize!T;
 
 	static if( is(T == class) ){