[rygel] Allow UI build without gstreamer-video

[Jens Georg <jensgeorg src gnome org>]

commit 5899cdfe9ff650eb8b71c2486154bc01a7629ffa
Author: Fabrice Fontaine <fontaine fabrice gmail com>
Date:   Mon Jan 8 21:38:54 2018 +0100

    Allow UI build without gstreamer-video
    
    If EXAMPLE_UI dependencies are not met, only display a warning instead
    of ending configure with an error.
    Indeed, currently, we can't build rygel UI without gstreamer-video which
    is only a dependency of fullscreen-renderer application.
    
    fullscreen-renderer won't be build without gstreamer as HAVE_GSTREAMER
    has to be true to check HAVE_UI in examples/Makefile.am
    
    Signed-off-by: Fabrice Fontaine <fontaine fabrice gmail com>
    
    https://bugzilla.gnome.org/show_bug.cgi?id=792358

 configure.ac |    6 +++++-
 1 files changed, 5 insertions(+), 1 deletions(-)
---
diff --git a/configure.ac b/configure.ac
index c51d580..b4ee95b 100644
--- a/configure.ac
+++ b/configure.ac
@@ -359,7 +359,11 @@ if test x$try_ui = xyes ; then
                           [$RYGEL_COMMON_MODULES gio-2.0 >= $GIO_REQUIRED
                            gssdp-1.0 >= $GSSDP_REQUIRED
                            gstreamer-video-1.0 >= $GSTREAMER_REQUIRED
-                           gtk+-3.0 >= $GTK_REQUIRED])
+                           gtk+-3.0 >= $GTK_REQUIRED],,
+                          [
+                           AC_MSG_WARN([Example UI dependencies not found.])
+                           AC_MSG_WARN([Example UI applications will not be built.])
+                          ])
       ],
       [
         AC_MSG_WARN([UI dependencies not found.])