ZoneCode: Add Action on loading a GfxImage to set the loadedSize property to 0 to indicate Texture data has not yet been loaded

src/ZoneCode/Game/T6/T6_Commands.txt

@@ -363,6 +363,7 @@ set reusable u::literalConst;
 // GfxImage
 // =========================================
 use GfxImage;
+set action OnImageLoaded(GfxImage);
 set string name;
 set name name;
 set condition pixels never;