[cheese] Properly quote $UDEV_REQUIRED variable, bug 673628

[David King <davidk src gnome org>]

commit 1d1aa7be13ab4705a1e8231fb194563cefb069be
Author: Michael Biebl <biebl debian org>
Date:   Fri Apr 6 10:31:45 2012 +0200

    Properly quote $UDEV_REQUIRED variable, bug 673628
    
    Otherwise configure fails on systems which don't have libgudev
    installed.

 configure.ac |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/configure.ac b/configure.ac
index b669799..874ab3f 100644
--- a/configure.ac
+++ b/configure.ac
@@ -88,7 +88,7 @@ AS_CASE([$host_os],
   [AC_MSG_RESULT([unsupported operating system])])
 
 AC_MSG_CHECKING([for gudev-1.0])
-AS_IF([test -n $UDEV_REQUIRED],
+AS_IF([test -n "$UDEV_REQUIRED"],
   [PKG_CHECK_EXISTS([$UDEV_REQUIRED],
     [AC_MSG_RESULT([found])
      AC_DEFINE([HAVE_UDEV], [], [Enable gudev support])],