avcodec/vp9dsp_template: Fix integer overflow in iadst8_1d()

Fixes: signed integer overflow: 998938090 + 1169275991 cannot be represented in type 'int'
Fixes: 23411/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_VP9_fuzzer-4644692330545152

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

libavcodec/vp9dsp_template.c

@@ -1260,20 +1260,20 @@ static av_always_inline void iadst8_1d(const dctcoef *in, ptrdiff_t stride,
     t6 = (t2a - t6a + (1 << 13)) >> 14;
     t7 = (t3a - t7a + (1 << 13)) >> 14;
 
-    t4a = 15137 * t4 +  6270 * t5;
-    t5a =  6270 * t4 - 15137 * t5;
-    t6a = 15137 * t7 -  6270 * t6;
-    t7a =  6270 * t7 + 15137 * t6;
+    t4a = 15137U * t4 +  6270U * t5;
+    t5a =  6270U * t4 - 15137U * t5;
+    t6a = 15137U * t7 -  6270U * t6;
+    t7a =  6270U * t7 + 15137U * t6;
 
     out[0] =   t0 + t2;
     out[7] = -(t1 + t3);
     t2     =   t0 - t2;
     t3     =   t1 - t3;
 
-    out[1] = -((t4a + t6a + (1 << 13)) >> 14);
-    out[6] =   (t5a + t7a + (1 << 13)) >> 14;
-    t6     =   (t4a - t6a + (1 << 13)) >> 14;
-    t7     =   (t5a - t7a + (1 << 13)) >> 14;
+    out[1] = -((dctint)((1U << 13) + t4a + t6a) >> 14);
+    out[6] =   (dctint)((1U << 13) + t5a + t7a) >> 14;
+    t6     =   (dctint)((1U << 13) + t4a - t6a) >> 14;
+    t7     =   (dctint)((1U << 13) + t5a - t7a) >> 14;
 
     out[3] = -(((t2 + t3) * 11585 + (1 << 13)) >> 14);
     out[4] =   ((t2 - t3) * 11585 + (1 << 13)) >> 14;