Strip effect breaks dimension calculation

When the Strip metadata (strip) effect from imagemagick_advanced.module is added to an image style, the dimension calculation performed by image_style_transform_dimensions() changes the width and height to NULL.

All effects that can be applied to images need to either provide a 'dimensions callback' or a 'dimensions passthrough' to state that the effect changes the image dimensions or that it has no effect on dimensions. As the strip effect currently doesn't provide either, width and height are set to NULL. This can be overcome by adding 'dimensions passthrough' to the strip effect declaration.

     'label' => t('Strip metadata'),
     'help' => t('Resizing will make images an exact set of dimensions. This may cause images to be stretched or shrunk disproportionately.'),
     'effect callback' => 'imagemagick_advanced_strip_effect',
+    'dimensions passthrough' => TRUE,
   );
   return $effects;

More information on the image style dimension calculation, and theme_image_style() where it is invoked.