properly load tga with top-left origin

Texture.h

@@ -58,7 +58,7 @@ private:
     void downsize( GLuint const Format );
 
 // members
-    std::vector<char> data; // texture data
+    std::vector<char> data; // texture data (stored GL-style, bottom-left origin)
     resource_state data_state{ resource_state::none }; // current state of texture data
     int data_width{ 0 },
         data_height{ 0 },