examples/dmabuf-capture: make building this example optional

examples/meson.build

@@ -1,9 +1,9 @@
 threads = dependency('threads')
 wayland_cursor = dependency('wayland-cursor')
 
-libavutil = dependency('libavutil')
-libavcodec = dependency('libavcodec')
-libavformat = dependency('libavformat')
+libavutil = dependency('libavutil', required: false)
+libavcodec = dependency('libavcodec', required: false)
+libavformat = dependency('libavformat', required: false)
 
 executable('simple', 'simple.c', dependencies: wlroots)
 executable('pointer', 'pointer.c', dependencies: wlroots)
@@ -43,8 +43,10 @@ executable(
 	dependencies: [wayland_cursor, wayland_client, wlr_protos, wlroots]
 )
 
+if libavutil.found() and libavcodec.found() and libavformat.found()
 	executable(
 		'dmabuf-capture',
 		'dmabuf-capture.c',
 		dependencies: [wayland_client, wlr_protos, libavutil, libavcodec, libavformat]
 	)
+endif