fix resource packs and add support for texture packs

Signed-off-by: Ryan Cao <70191398+ryanccn@users.noreply.github.com>

launcher/minecraft/mod/TexturePack.h

@@ -48,6 +48,8 @@ class TexturePack : public Resource {
     /** Thread-safe. */
     void setImage(QImage new_image);
 
+    bool valid() const override;
+
    protected:
     mutable QMutex m_data_lock;