libgui|ModelDrawable: Commit textures are initialization complete

When using IAtlas, commit() is expected after all the images have been
allocated. MultiAtlas::AllocGroup will then decide on which atlas to
actually place the allocations.

doomsday/sdk/libgui/src/graphics/modeldrawable.cpp

@@ -470,6 +470,8 @@ DENG2_PIMPL(ModelDrawable)
                     fallBackToDefaultTexture(textures, Emissive);
                 }
             }
+            // All textures loaded.
+            textureBank.atlas()->commit();
         }
 
         /**