avcodec/mpegvideo: Clear pointers in ff_mpv_common_init()

This ensures that no stale pointers leak through on any path

Fixes: signal_sigsegv_c3097a_991_xtrem_e2_m64q15_a32sxx.3gp

Found-by: Samuel Groß, Mateusz "j00ru" Jurczyk and Gynvael Coldwind
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
(cherry picked from commit b160fc29)
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/mpegvideo.c

@@ -1286,6 +1286,82 @@ fail:
     return AVERROR(ENOMEM);
 }
 
+static void clear_context(MpegEncContext *s)
+{
+    int i, j, k;
+
+    memset(&s->next_picture, 0, sizeof(s->next_picture));
+    memset(&s->last_picture, 0, sizeof(s->last_picture));
+    memset(&s->current_picture, 0, sizeof(s->current_picture));
+    memset(&s->new_picture, 0, sizeof(s->new_picture));
+
+    memset(s->thread_context, 0, sizeof(s->thread_context));
+
+    s->me.map = NULL;
+    s->me.score_map = NULL;
+    s->dct_error_sum = NULL;
+    s->block = NULL;
+    s->blocks = NULL;
+    memset(s->pblocks, 0, sizeof(s->pblocks));
+    s->ac_val_base = NULL;
+    s->ac_val[0] =
+    s->ac_val[1] =
+    s->ac_val[2] =NULL;
+    s->edge_emu_buffer = NULL;
+    s->me.scratchpad = NULL;
+    s->me.temp =
+    s->rd_scratchpad =
+    s->b_scratchpad =
+    s->obmc_scratchpad = NULL;
+
+    s->parse_context.buffer = NULL;
+    s->parse_context.buffer_size = 0;
+    s->bitstream_buffer = NULL;
+    s->allocated_bitstream_buffer_size = 0;
+    s->picture          = NULL;
+    s->mb_type          = NULL;
+    s->p_mv_table_base  = NULL;
+    s->b_forw_mv_table_base = NULL;
+    s->b_back_mv_table_base = NULL;
+    s->b_bidir_forw_mv_table_base = NULL;
+    s->b_bidir_back_mv_table_base = NULL;
+    s->b_direct_mv_table_base = NULL;
+    s->p_mv_table            = NULL;
+    s->b_forw_mv_table       = NULL;
+    s->b_back_mv_table       = NULL;
+    s->b_bidir_forw_mv_table = NULL;
+    s->b_bidir_back_mv_table = NULL;
+    s->b_direct_mv_table     = NULL;
+    for (i = 0; i < 2; i++) {
+        for (j = 0; j < 2; j++) {
+            for (k = 0; k < 2; k++) {
+                s->b_field_mv_table_base[i][j][k] = NULL;
+                s->b_field_mv_table[i][j][k] = NULL;
+            }
+            s->b_field_select_table[i][j] = NULL;
+            s->p_field_mv_table_base[i][j] = NULL;
+            s->p_field_mv_table[i][j] = NULL;
+        }
+        s->p_field_select_table[i] = NULL;
+    }
+
+    s->dc_val_base = NULL;
+    s->coded_block_base = NULL;
+    s->mbintra_table = NULL;
+    s->cbp_table = NULL;
+    s->pred_dir_table = NULL;
+
+    s->mbskip_table = NULL;
+
+    s->er.error_status_table = NULL;
+    s->er.er_temp_buffer = NULL;
+    s->mb_index2xy = NULL;
+    s->lambda_table = NULL;
+
+    s->cplx_tab = NULL;
+    s->bits_tab = NULL;
+}
+
 /**
  * init common structure for both encoder and decoder.
  * this assumes that some variables like width/height are already set
@@ -1297,6 +1373,8 @@ av_cold int ff_mpv_common_init(MpegEncContext *s)
                      s->avctx->active_thread_type & FF_THREAD_SLICE) ?
                     s->avctx->thread_count : 1;
 
+    clear_context(s);
+
     if (s->encoding && s->avctx->slices)
         nb_slices = s->avctx->slices;
 
@@ -1344,10 +1422,6 @@ av_cold int ff_mpv_common_init(MpegEncContext *s)
         if (!s->picture[i].f)
             goto fail;
     }
-    memset(&s->next_picture, 0, sizeof(s->next_picture));
-    memset(&s->last_picture, 0, sizeof(s->last_picture));
-    memset(&s->current_picture, 0, sizeof(s->current_picture));
-    memset(&s->new_picture, 0, sizeof(s->new_picture));
     s->next_picture.f = av_frame_alloc();
     if (!s->next_picture.f)
         goto fail;