vc1dec: add flush function for WMV9 and VC-1 decoders

CC: libav-stable@libav.org
(cherry picked from commit 4dc8c8386e)

Signed-off-by: Anton Khirnov <anton@khirnov.net>

libavcodec/vc1dec.c

@@ -3834,7 +3834,8 @@ AVCodec ff_vc1_decoder = {
     .flush          = ff_mpeg_flush,
     .long_name = NULL_IF_CONFIG_SMALL("SMPTE VC-1"),
     .pix_fmts = ff_hwaccel_pixfmt_list_420,
-    .profiles = NULL_IF_CONFIG_SMALL(profiles)
+    .profiles = NULL_IF_CONFIG_SMALL(profiles),
+    .flush = ff_mpeg_flush,
 };
 
 #if CONFIG_WMV3_DECODER
@@ -3852,7 +3853,8 @@ AVCodec ff_wmv3_decoder = {
     .flush          = ff_mpeg_flush,
     .long_name = NULL_IF_CONFIG_SMALL("Windows Media Video 9"),
     .pix_fmts = ff_hwaccel_pixfmt_list_420,
-    .profiles = NULL_IF_CONFIG_SMALL(profiles)
+    .profiles = NULL_IF_CONFIG_SMALL(profiles),
+    .flush = ff_mpeg_flush,
 };
 #endif