[gthumb] fixed build if appstream >= 0.14.6 is not available

[Paolo Bacchilega <paobac src gnome org>]

commit c59f19509b32d980024ae4e15803d7d383afd970
Author: Paolo Bacchilega <paobac src gnome org>
Date:   Wed Dec 8 18:03:04 2021 +0100

    fixed build if appstream >= 0.14.6 is not available

 data/meson.build | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)
---
diff --git a/data/meson.build b/data/meson.build
index b09494da..5fe973dd 100644
--- a/data/meson.build
+++ b/data/meson.build
@@ -54,7 +54,9 @@ gthumb_pc = pkg.generate(
 
 # Subdirectories
 
-subdir('appdata')
+if dependency('appstream', version : '>=0.14.6', required : false).found()
+  subdir('appdata')
+endif
 subdir('gschemas')
 subdir('icons')
 subdir('ui')