Fix VDPAU check to avoid printing spurious messages to the console.

Originally committed as revision 21016 to svn://svn.ffmpeg.org/ffmpeg/trunk

configure

@@ -2500,11 +2500,12 @@ check_func XOpenDisplay -lX11           &&
 check_func XShmCreateImage -lX11 -lXext &&
 check_func XFixesGetCursorImage -lX11 -lXext -lXfixes
 
-enabled vdpau_vdpau_h &&
+if enabled vdpau_vdpau_h; then
 check_cpp_condition \
     vdpau/vdpau.h "defined VDP_DECODER_PROFILE_MPEG4_PART2_ASP" ||
     { echolog "Please upgrade to libvdpau >= 0.2 if you would like vdpau support." &&
       disable vdpau; }
+fi
 
 enabled debug && add_cflags -g"$debuglevel" && add_asflags -g"$debuglevel"