avcodec/msmpeg4dec: init dc_pred_dir

Its not really used but its passed as a argument and then not used
Fixes: 70965/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_MSMPEG4V1_fuzzer-5583223747313664

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/msmpeg4dec.c

@@ -628,7 +628,7 @@ int ff_msmpeg4_decode_block(MpegEncContext * s, int16_t * block,
                               int n, int coded, const uint8_t *scan_table)
 {
     int level, i, last, run, run_diff;
-    int av_uninit(dc_pred_dir);
+    int dc_pred_dir = -1; //unused but its passed around, so it needs to be initialized
     const RLTable *rl;
     const RL_VLC_ELEM *rl_vlc;
     int qmul, qadd;