As of Drupal 7.50 don't drupal_get_path of a non-existing module

[scottrigby]

In kalatheme_css_alter() there are several calls to drupal_get_path() for modules that may not exist on the user's system. If not, as of Drupal 7.50 a warning will be issued "The following module is missing from the file system" (see https://www.drupal.org/node/2487215 and the change record). I'll make a patch wrapping those in module_exists(), which clears up the problem.

[RobLoach]

Beat me to it! If you submit that PR, I'll merge.