[gxml] No build docs on valadoc not found

[Daniel Espinosa Ortiz <despinosa src gnome org>]

commit 2675e03867f814f6413a97d80ed040e69e46b392
Author: Daniel Espinosa <esodan gmail com>
Date:   Wed Nov 22 15:06:56 2017 -0600

    No build docs on valadoc not found

 docs/meson.build |    4 +++-
 1 files changed, 3 insertions(+), 1 deletions(-)
---
diff --git a/docs/meson.build b/docs/meson.build
index 25e8e5d..52b2aa5 100644
--- a/docs/meson.build
+++ b/docs/meson.build
@@ -1,4 +1,5 @@
-valadoc = find_program ('valadoc')
+valadoc = find_program ('valadoc', required: false)
+if valadoc.found()
 outdir ='GXml-'+API_VERSION
 gtkdoc_outdir ='gxml-'+API_VERSION
 valacapi = run_command ('valac', '--api-version')
@@ -30,3 +31,4 @@ custom_target ('valadocs',
                        valasources],
                install : true,
                install_dir : docsdir)
+endif