XEEN: Add Virtual Destructor to SpritesDrawer Base Class

This is required to avoid GCC Compiler Warnings from -Wnon-virtual-dtor

engines/xeen/sprites.h

@@ -196,6 +196,11 @@ public:
 	 */
 	SpriteDrawer(byte *data, size_t filesize) : _data(data), _filesize(filesize) {}
 
+	/**
+	 * Destructor
+	 */
+	virtual ~SpriteDrawer() {}
+
 	/**
 	 * Draw a sprite frame based on a passed offset into the data stream
 	 */