fate/lavf-container: Check earlier for presence of ffmpeg cli

Several other tests (e.g. concatdec) examine FATE_LAVF_CONTAINER
in order to enable or disable tests that depend on samples
created by the lavf-container tests; right now this procedure
did not account for CONFIG_FFMPEG.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>

tests/fate/lavf-container.mak

@@ -30,7 +30,7 @@ FATE_LAVF_CONTAINER_SCALE := dv dv_pal dv_ntsc flm gxf gxf_pal gxf_ntsc \
 FATE_LAVF_CONTAINER-$(!CONFIG_SCALE_FILTER) := $(filter-out $(FATE_LAVF_CONTAINER_SCALE),$(FATE_LAVF_CONTAINER-yes))
 
 FATE_LAVF_CONTAINER = $(FATE_LAVF_CONTAINER-yes:%=fate-lavf-%)
-FATE_LAVF_CONTAINER := $(if $(call ENCDEC2, RAWVIDEO PGMYUV, PCM_S16LE, CRC IMAGE2, PCM_S16LE_DEMUXER PIPE_PROTOCOL), $(FATE_LAVF_CONTAINER))
+FATE_LAVF_CONTAINER := $(if $(call ENCDEC2, RAWVIDEO PGMYUV, PCM_S16LE, CRC IMAGE2, PCM_S16LE_DEMUXER PIPE_PROTOCOL FFMPEG), $(FATE_LAVF_CONTAINER))
 
 $(FATE_LAVF_CONTAINER): CMD = lavf_container
 $(FATE_LAVF_CONTAINER): REF = $(SRC_PATH)/tests/ref/lavf/$(@:fate-lavf-%=%)