avcodec/truemotion2: Fix several integer overflows in tm2_update_block()

Fixes: signed integer overflow: -1877966852 + -469491713 cannot be represented in type 'int'
Fixes: 14561/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_TRUEMOTION2_fuzzer-5167608359288832

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit 8eecf761a6)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/truemotion2.c

@@ -688,15 +688,15 @@ static inline void tm2_update_block(TM2Context *ctx, AVFrame *pic, int bx, int b
     TM2_RECALC_BLOCK(V, Vstride, (clast + 2), (ctx->CD + 2));
 
     /* update deltas */
-    ctx->D[0] = Yo[3] - last[3];
-    ctx->D[1] = Yo[3 + oYstride] - Yo[3];
-    ctx->D[2] = Yo[3 + oYstride * 2] - Yo[3 + oYstride];
-    ctx->D[3] = Yo[3 + oYstride * 3] - Yo[3 + oYstride * 2];
+    ctx->D[0] = (unsigned)Yo[3] - last[3];
+    ctx->D[1] = (unsigned)Yo[3 + oYstride] - Yo[3];
+    ctx->D[2] = (unsigned)Yo[3 + oYstride * 2] - Yo[3 + oYstride];
+    ctx->D[3] = (unsigned)Yo[3 + oYstride * 3] - Yo[3 + oYstride * 2];
 
     for (j = 0; j < 4; j++) {
         d = last[3];
         for (i = 0; i < 4; i++) {
-            Y[i]    = Yo[i] + GET_TOK(ctx, TM2_UPD);
+            Y[i]    = Yo[i] + (unsigned)GET_TOK(ctx, TM2_UPD);
             last[i] = Y[i];
         }
         ctx->D[j] = last[3] - d;