[tali] meson: add missing line from previous commit

[Jeremy Bicha <jbicha src gnome org>]

commit 31672dfabe25daa5155ca0c84353b44613df9013
Author: Jeremy Bicha <jbicha ubuntu com>
Date:   Sun Jan 20 22:02:39 2019 -0500

    meson: add missing line from previous commit

 data/meson.build | 1 +
 1 file changed, 1 insertion(+)
---
diff --git a/data/meson.build b/data/meson.build
index a9e65d5..78d49c1 100644
--- a/data/meson.build
+++ b/data/meson.build
@@ -33,6 +33,7 @@ desktop_file = i18n.merge_file ('desktop-file',
                  po_dir: '../po',
                  type: 'desktop')
 
+desktop_file_validate = find_program('desktop-file-validate', required: false)
 if desktop_file_validate.found()
   test(
     'validate-desktop',